Experimental Studies on Biological Individuality Utilizing Marine Invertebrates

If Sponges Could Express Themselves: Experimental Studies on Biological Individuality Utilizing Marine Invertebrates, ca, 1900-1935

“My own suspicion is that the world is not only queerer than we suppose, but queerer than we *can* suppose”^[1]

Introduction

This quotation from the biologist J.B.S. Haldane exemplifies the depth of knowledge gained from peering into and understanding the complex and at times queer mechanisms of biological processes.^[2] The twentieth century made significant strides in several fields including genetics and evolutionary biology. In the early part of the century one of the less significant areas at the time, experimental invertebrate zoology, was yet to make its mark on history. However, this field of biology had quite an impact on the philosophical notion of biological individuality. David Valle defines individuality as the natural qualities that distinguish one entity from another.^[3] These include variations within the body or in cellular structure and function. Individuality is an ambiguous term, as there are currently many ways to describe an individual. Scientists and philosophers have debated this issue since antiquity and offered competing definitions. ^[4]

The two most important definitions of individuality are the organism-centered view and the life cycle view. Until the nineteenth century philosophers and scientists relied mostly on the naked eye using morphology, dissection, and embryology to distinguish individuality. The observational view in antiquity, guided in large part by Aristotle’s musings on individuality, was that the single organism was born, became sexually mature and reproduce, and then dies.  At the turn of the nineteenth century, philosophers of biology began to examine the role that life cycles have played in this organismal view. In some instances, like that of the jellyfish, a free-swimming medusa (adult) form alternated with a sessile polyp (offspring) form. This alternation meant that during its life cycle it could switch between a polyp and a medusa, which upended linear views of the single organism.^[5] It was in the twentieth century that these criteria became even shakier when individual organisms, like the jellyfish, were discovered to be composed of colonies of organisms, each seemingly acting on their own accord. Colonial animals also posed definitional challenges to the concept of the individual. This was particularly the case with sponges.

This paper analyzes two major case studies, the experiments of Henry Van Peters Wilson, and those of Julian Huxley.^[6][7]  Both men investigated the concept of biological individuality in the laboratory by dissociating sponge cells.  These significant experiments enabled biologists to assess whether individual sponge cells, which had the property to regenerate other cells or the whole sponge, constituted an individual.

Henry Van Peters Wilson

Before delving into biological individuality, it would be best to understand who Wilson was and how his work fits into the landscape of Gilded Age biology.  A relatively obscure figure in the history of biology, Henry Van Peters Wilson was born in Baltimore, Maryland, in 1863. Neither his father nor mother were scientists. After attending Baltimore City College, Wilson entered Johns Hopkins University intent on studying medicine.^[8][9] He soon shifted to zoology and became a private tutor to several prominent Maryland families.  After completing his dissertation on marine embryology in 1888, Wilson held a series of positions. For example, he went to the Bahamas to study sponges and found work as a scientific assistant at the U.S. Fish Commission’s facility in Woods Hole, Massachusetts. All the while, he was developing a publishable article based on his dissertation research entitled Embryology of the Sea Bass (Serranus atrarius) under the mentorship of William Keith Brookes, completed in 1891, which provided a classic study of vertebrate embryology and contained excellent illustrations^[10][11][12].

The positions he held, and his manuscript caught the eye of the University of North Carolina at Chapel Hill and the burgeoning Zoology department at the time asked Wilson to be the University’s first Professor of Zoology in the University’s Biology Department^[13]. Within the same year of publishing his manuscript, Wilson accepted the position and moved to Chapel Hill where he remained active in teaching and research until his death. Accounts of Wilson’s work ethic and personality portray him as dedicated and strong-willed.^[14] His biographer, Donald Costello, describes a man who made  “his way by foot through muddy streets to ill-equipped laboratories with very basic equipment.”^[15] He was a man of dynamic personality, and because he had been one of the University’s few professors in the Department of Zoology, he had a quite a bit on his plate.

He had to manage a department of zoology on little or no pecuniary means, teach large numbers of undergraduate students without an adequate amount of instructors, assistants or proper equipment, and to continue to carry on significant research at a level eliciting praise from his colleagues in this country and abroad, in an institution where research was considered to be of considerably less importance than routine teaching and where it was permitted that a professor devoted his spare time (if any), holidays, and summers (without salary) to his research.^[16]

The Department of Zoology at the University of North Carolina noted Wilson’s dedication to his work and awarded him the title of Keenan Professor of Zoology in 1929. Allowed a year’s leave, Wilson spent a majority of his time at the Stazione Zoologica at Naples where he conducted a series of experiments examining the metamorphosis of halichondria sponge larvae.^[17]

Figure 1. Photograph of Henry Van Peters Wilson, Director of Biological Laboratory at Beaufort, North Carolina.(http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/wilson-henry.pdf)/

He later taught and did research at the United States Fisheries Department’s marine station, housed in Beaufort, North Carolina.^[18] He spent almost all of his time at the station, and it was here that he conducted his most important experiments. He would publish more than ninety articles in his lifetime.^[19] These experiments garnered praise from colleagues and biologists from across the nation. The recognition he received for his work created a series of correspondences with other biologists, most notably with the Harvard museum administrator and marine biologist, Alexander Agassiz.^[20] In 1903, Agassiz contacted Wilson to review and identify sponges that had been collected by an oceanographic expedition, the USS Albatross.^[21] By the time of his death, in 1939, Wilson would be known as one of the world’s foremost authorities on sponges. Former Keenan Professor of Zoology and one of many Wilson’s biographers, Donald Costello wrote, “he was not a man lightly to tolerate fools among his colleagues, assistants, or students. He expected efficiency, almost approaching perfection, in others as well as in himself, and worked with tireless energy to attempt to achieve this end.”^[22] He was also a jovial man, whom his students had affectionately nicknamed ‘Froggy,’ as he would spend much of his time at the marine laboratory at Beaufort. As one of his former students remarked: “the Beaufort Laboratory was his child, his joy and pet … it was at Beaufort that we came to know the man as something more than the teacher.”^[23] The station had become a special place for Wilson, as he felt much pride in his creation. Wilson’s contribution to UNC’s scientific profile was significant, and in 1939, the year Wilson died, the university christened a Wilson Hall to serve as the Biology Department’s offices. Wilson’s colleague and fellow biologist at UNC Ronald E. Coker spent a considerable amount of his time creating a Memorial Fund and collecting Wilson’s papers.^[24][25][26] His most famous paper as regards to the individuality question was his  “On Some Phenomenon of Coalescence and Regeneration in Sponges” of 1907.^[27]

Henry Wilson’s 1907 experiment

Wilson’s 1907 article is considered to be his most widely cited article.  The paper made a significant contribution to the understanding of biological individuality. It described an investigation by Wilson, and conducted at the university, utilizing a unique methodology and set of materials at the time.

Wilson’s experimental subject was a species of sponge, Microciona prolifera, which grew in abundance in North Carolina. Wilson cut and crumbled the sponge into tiny pieces and forced the fragments through a fine metal sieve. By disintegrating the sponge body, it separated the sponge’s constituent cells so that they were physically isolated from others. After being torn apart, Wilson placed the dissociated cells in a bucket of saltwater. When the cells; finally, settled along the bottom, a remarkable phenomenon occurred.^[28] Wilson wrote that the “fusion of granular cells began immediately and in a few minutes time most of them have united to form small conglomerate masses.”^[29] The sponge cells uniting after being disaggregated is observed in Figure 2 below. Figure 2 shows the “larvae,” or the individual sponge cells, fusing to become what Wilson refers to as “perfect sponges.”^[30] Wilson numbered them because the cells had formed different shapes when they were in the process of fusing together.^[31]

Figure 2: Larva fusing to create whole, functional sponges. Note the different shapes as they blend, which Wilson suggested was distinct for each differentiated sponge cell that fuses. (https://archive.org/details/cbarchive_34897_onsomephenomenaofcoalescencean9999)

Within about three days time, the cells had reunited and differentiated into their component functions. The dermal cells situated themselves on the exterior of the sponge, and the flagellated chambers on the interior, thereby creating a functional sponge.^[32][33] However, one should note that Wilson’s paper did not explore the implications of the regeneration phenomena by remarking on the possibility of biological individuality. While Wilson’s article did not fully explore the broader and deeper philosophical issues, he did note, “to such a mass, the ordinary idea of the individual is not applicable.”^[34]

Wilson developed his philosophical musings on individuality in a lesser-known work entitled “The Nature of The Individual in The Animal Kingdom,” which was a transcript of lectures delivered from 1915-1916, which he published in Journal of the Elisha Mitchell Scientific Society on April 1917. In these lectures, Wilson described an experiment he conducted on a sponge’s ability to adapt to certain environments. When he kept a sponge “in confinement under conditions that are unfavorable and yet not immediately disastrous, the sponge body quickly [gave] up much of its structure.”^[35] When Wilson lowered the calcium content of the container, the cells within began to adapt to the changing surroundings as the sponge endeavored to protect itself. Wilson found that if one continues to subject the sponge to unfavorable conditions that it “ceases to act as an individual. A large part of it dies. Cells creep together in spots and form little masses easily distinguishable by their bright color.”^[36] Wilson then began to speculate on the philosophical significance of his experiment. He saw that the sequence of events, from the cells breaking apart from a complex and dying organism to the formation into separate constituent masses, was illustrative of a long-held view of individuality. This view was known as the parts and the whole concept.^[37] Wilson perceived the sponge as abandoning its individualism and breaking into masses each capable of producing new individuals. Wilson’s discoveries led another biologist, Julian Huxley, to pursue further research on the subject.

Julian Huxley’s 1912 Experiment

Huxley’s experiments on sponge cells and their implications for biological individuality require a working understanding of a few concepts: the notion of parts and wholes, and group selection theory. The parts and wholes concept is a physiological view of animal individuality which regards the organism as comprised of components that cooperate for the good of the whole. The general idea had been developed and elaborated by the nineteenth-century French physiologist Claude Bernard who applied the notion to cellular function. The whole operates as a system of interconnected parts, each serving a purpose. The second notion is group selection theory. Group selection theory is a somewhat contentious view of natural selection, and acts collectively on all members of a given group instead of working on the level of the individual.^[38][39] The theory is now being used to explain many of biology’s most vexing mysteries, “including the nature of individuality and the major transitions in evolutionary history.”^[40] Building on some of Wilson’s findings Huxley explained logical connections between the theory of group selection and the concepts of biological individuality.

In 1909, the twenty-year-old Julian Huxley accepted a fellowship to work at the Marine Zoological Station in Naples, Italy. There he replicated Wilson’s experiment using the Sycon genus of the sponge, which allowed him to cultivate cells that were larger than those in Wilson’s and experiments and larger cells enabled him to watch their migration across the auger plate without having to rely on dying techniques or having to acquire different species of sponges.[41] Following Wilson’s methodology, Huxley crushed the sponge into tiny pieces and forced the fragments through the sieve. After extracting the contents, he examined them under a microscope to confirm Wilson’s results. Huxley found that Wilson’s conclusions were accurate and stressed that the cells not only survived their severance from one another but also the new arrangement did not seem to disturb them. The level of autonomy displayed by the disaggregated cells convinced Huxley that they possessed all the hallmarks of true individuality, which he believed to be individual constituent parts of the sponge re-aggregating for the benefit of the group or the whole sponge.^[42]  In his essay entitled, “The Biological Basis of Individuality” Huxley noted that though the “whole sponge is a true individual, composed of harmonious parts, yet those parts could themselves behave as harmonious wholes.”^[43]

Huxley’s theory of sponge coalescence acts as a premier example of the parts and the whole concept of individuality and works in conjunction with early twentieth century understandings of biological cooperation. However, this was not his only revelation in his 1912 essay, as he later described how the dissociated cells moved across the bottom of the tank in an amoeboid fashion, finally joining together to form a globule of cells. Then, specific cells that served certain functions, such as collar cells and dermal cells in the sponge, began to sort themselves out. In several days time, this random collection of cells became “an actual sponge, living, and functioning, similar in every way to one that has grown up from the egg.”^[44] Huxley concluded that the cells seemed to be subject to a higher individuality. He observed, “there seemed to be a strange organizing power superior in kind to the power of the cells themselves- an idea of the whole informing the parts.”^[45] This self-minded organization puzzled him as he attempted a second experiment to discern what compelled these individual cells to unite.^[46] Figure 3, featured in the next page, shows the coalescence of its collar cells, the filter-feeding cells of the sponge. These cooperate to form what Huxley referred to as Proterospongia, or “colonies of a single layer of cells that form a curved plate or sphere of cells.^[47] Huxley’s experiment essentially revealed individual cells were forming a multicellular whole.^[48][49] Separating would decrease the amount of food each collar cell could gather. Cooperating is not only safe for a single collar cell, but it is economical as the ability to share food amongst themselves maximizes its survival value thereby minimizing potential risk. It is similar to how Gorgonians operate. Gorgonians are sessile colonial cnidarians that live in many of the world’s oceans. They are composed of multiple individual polyps that combine on a substrate to cooperate for the survival of the whole.^[50]

Figure 3. This image from Huxley’s evolutionary-centered article illustrates the coalescence of collar cells from a sponge as they form a multicellular whole. (http://rstb.royalsocietypublishing.org/content/royptb/202/282-293/165.full.pdf)

Huxley believed the answer resided in a mysterious and latent process in the evolutionary history of life. To prove this, Huxley modified the variables of Wilson’s experiment by isolating dissociated collar cells from the body of the sponge.  The specialized cells formed a spherical mass, which he interpreted as “evidence that sponges are descended from cells which existed as free-living and independent individuals.”^[51] Huxley explained that these cells, far in their evolutionary past, must have ceded more of their individuality to the colony that is formed, thereby enabling multi-cellularity.^[52] Huxley observed, “each cell preserves a considerable measure of independence and is yet subordinated to the good of the whole.”^[53] Once cooperation existed, competition between cooperative units would be necessary to increase the efficiency of their combination. Huxley explained that this is an inherent evolutionary need for organisms that express specific regenerative abilities, like sponges, and that it is therefore advantageous after dissociation to have its cells function and cooperate instead of the more likely option, dying as constituent parts. Huxley’s utilization of early twentieth century group selection and the concept of the parts and the whole allowed him to create a more nuanced framework of individuality that strayed from the organism-centered view and the life-cycle criteria, towards an evolutionary interpretation of this subject.

The notion of an evolutionary individual is now a more detailed version than Huxley’s original design. The contemporary philosopher of science, Peter Godfrey-Smith, has suggested: “that the distinction between a clump of cells and a multicellular organism is not a categorical dichotomy but one best situated along a continuum.”^[54] In one case, Godfrey-Smith refers to an evolutionary individual as a Darwinian individual, “meaning that they can form populations capable of undergoing evolution by natural selection, as occurs in the case of cancer.”^[55] Smith seems to build on Huxley’s idea of the evolutionary individual by stating that cells can in some cases be de-Darwinized, in which the cells become subservient parts to the whole organism. It is in this context that Huxley’s second experiment can be understood in an evolutionary context as the de-Darwinized cells of the sponge ceded their individuality to be subservient for the good of the organism. Huxley applied this framework derived from his sponge experiments throughout the biological hierarchy, from genes and organelles to populations and communities, indicating that they “are all levels of individuality.”^[56][57]

The use of group selection theory, or cooperation, in defining biological individuality allowed for a multitude of discoveries. It enabled philosophers and biologists to create a criterion of what an individual was and applied it to the investigation of other organisms, beyond sponges. Embryological studies of the adhesive and dissociative properties of chick and amphibian embryos have prompted further queries into the nature of individuality, creating a more complex criterion at the cellular level of organisms in which individual cells can group for the benefit of the whole.  This newer and experimental view of individuality, combined aspects of Aristotle’s philosophy of observations that viewed individuality as a single organism being born, becoming sexually mature and dying, to one found in nature.

It should be noted that the experimental manipulations described above weren’t relegated to the early twentieth century. In the 18th century, Abraham Trembley studied regeneration in hydra species in an attempt to determine whether the species he was studying was taxonomically, “either a plant (which regenerates) or an animal (which does not).”^[58] Trembley had established an experimental methodology of manipulating living organisms to answer complex biological phenomenon. In some ways, Trembley’s methods mirror that of Wilson and Huxley as they used the regenerative ability of sponges to understand. A past experimenter that used a methodology similar to Wilson’s initial experiment was the 19th-century German biologist Wilhelm Roux. Roux, using the blastomere of frog eggs instead of sponge cells, described a similar phenomenon to Wilson’s. At its early stages of segmentation, Roux separated the blastomeres, which then slowly approached one another until they finally came into contact.^[59]

The Sponge – A Model Organism

This paper highlights a shift in notions of biological individuality from a conception threading the needle between philosophy and natural philosophy, or observation, to a more experimental view.  However, this might not have been possible had it not been for a singular experimental subject, the sponge. Though much of the paper has described Wilson and Huxley’s experiments on the sponges as well as their philosophical musings on the nature of individuality as it relates to sponges, to say that the sponge was not an experimental organism, or at least much of a consequence, prior to Wilson’s work would be to discount the number of biologists that have utilized the marine invertebrate to illuminate the sponge’s anatomical and physiological nature as well as its dynamic cellular activity. The sponge’s compelling history dates back to the 16th century, however its use as an experimental organism to illuminate complex concepts like biological individuality began in the 19th century. In 1862, Oscar Schmidt, described in a series of memoirs how the sponge body manufactures spicules, which acts as the backbone for the sponge. He also noticed that if one cut up the body of a sponge, the parts would attach themselves to other cells and grow as new individuals.[60] Another example of the intersection of individuality and the sponge’s experimental use is the famed biologist Ernst Haeckel who, in 1872, used sponges to as the basis of his Colonial theory. The theory described a series of forms early on in the evolutionary history of life in which ancient and simple single-celled individuals ceded their individuality to form a colonial, multicellular individual, more commonly known as a sponge.[61] To examine and explain the theory, Haeckel used the flagellated cells, or the collar cells, of sponges. The cells mirrored what Haeckel believed early evolutionary transition would look like as the cells had cooperated to form a multicellular organism. These two experiments are clear precursors to the methodology, and the level of analysis displayed by both Wilson and Huxley, as they used 19th-century techniques and theories to push the boundaries of the century’s queries on individuality. Though the complexity of the sponge as an experimental tool was something biologist’s at the time understood, the same is not true for contemporary historians of biology.

As a whole, the historiography of sponges, as it relates to the history of biology, is lacking. As Wilson once wrote in his 1932 essay entitled Sponges and Biology, “if sponges could express themselves… I think a well-speaking sponge might address biologists somewhat in the following fashion: ‘I realize that we are not as widely known as some others and yet I feel that… we are not an uninteresting race.’”^[62]  When tackling this issue, historians of science like Robert Richards and Lynn Nyhart have viewed the sponge as a smaller player in the broader history of modern biology. Both describe the sponge’s taxonomy, morphology, and evolution. They have also noted its contribution to the celebrated embryologist Ernst Haeckel’s theory that embryology and evolutionary biology are linked and not different subjects.^[63] These examples emphasize the sponge’s features but do not actively showcase its role as a model organism.^[64] Even Endersby’s book, A Guinea Pig’s History of Biology, which tracks the history of biology through the intersection of classic model organism studies and cultural history, only touches on sponges.^[65][66] In it, Endersby relates that noted embryologist Elie Metchnikoff used sponges, and other invertebrates as a platform to study the inner workings’ immunology using specialized cells, or phagocytes. Metchnikoff’s utilization of sponge cells shows that sponges played at least some role in the understanding of immunity. Although Richards, Nyhart, and Endersby portray the study of sponges as a persistent but marginal activity, their importance was realized by a number of twentieth-century biologists including Wilson’s contemporary, the Russian marine biologist and embryologist, Paul Galtsoff.

Galtsoff studied self and non-self recognition in sponges. In 1923 he replicated one of Wilson’s experiments with two different species of sponges, Reniera informis and Reniera densa, with different colors. Both sponges were different colors with one being red and the other being yellow, and crumbled them both into a solution and determined that “cells of two different species of sponges mixed coalesce only with cells of their species.”^[67] Galtsoff was amazed by this discovery and attempted to tease out more of this ability to discern foreign elements. He also tagged both sponges with inks and died. The first part of the experiment tried to artificially press the sponges together by centrifuging them in mixed suspension.^[68] This test did not achieve full coalescence with the cells of another species, only a clump of loosely mixed cells. Galtsoff analyzed the cluster after 24 hours and found the yellow mass of sponge cells had formed globular aggregates with marked membranes separating them from cells of the other species. The yellow sponge species also produced cytotoxic enzymes that caused damage to the other species. Additionally, the yellow sponge created a barrier around itself. Galtsoff concluded that the sponge cells could recognize their species, or self, from others not of their species (or non-self).^[69] Figure 4, featured in the next page, showcases the immunological ability of sponges through a rather simple diagram. The diagram shows how different sponge species, after dissociation, can recognize their own from different cells.^[70][71]

Figure 4. The diagram portrays the process by which different species of sponge cells individually sort out when in proximity to one another. When two unrelated species are mechanically dissociated into a single-cell suspension, they will in due time sort out in two separate sponge cell clumps of the original species. In the diagram, the rectangular species can be thought of as one of Galtsoff’s Renaria genus and the triangular species Wilson’s Microciona prolifera. The spikes for each representing the necessary surface material needed for specific re-aggregation. It is through these cell surface components that the cells can distinguish self from non-self. (http://rstb.royalsocietypublishing.org/content/royptb/271/912/379.full.pdf)

The immunological ability of cells to distinguish between self and non-self is itself not new to early twentieth century biology. Likely one of the first scientists to illuminate to the scientific world the existence of this phenomenon in the 19^th century was Paul Ehrlich, who had analyzed tissues in human bodies and explained how the body produces what he calls ‘amboceptors’, commonly referred to as antibodies, which were directed against certain tissues that had been compromised. Though the phenomenon was well known by the time of Galtsoff’s experiment on the two sponges, the ability of the sponge organism or even its individual cells to be able to determine self from non-self, utilizing some form of immunological ability showcases its versatility as an experimental subject, being utilized to solve some of biology’s most vexing problems outside of biological individuality and regeneration. ^[72]

The basis of immunology is the idea that the body can determine self from non-self through the use of specific macromolecules. This ability is similar to a classic example of immunology, the antibody, and corresponding antigen. When a foreign body infects the human body, an attempt is made to correct the imbalance and react to the appearance of alien macromolecules, or a combination of macromolecules, by creating antibodies.^[73]  The antibody physically attaches itself to the corresponding antigen of the invader. The binding of the antibody to an antigen, a physical binding, is the principal way in which the human body neutralizes invaders.^[74] By combining with the antigen, the antibody makes it easier for the phagocytes to ingest the invaders. The invader’s antigens expedite the process of phagocytosis, or the eating of cells is made easier by the presence of antibody. The reaction of the cell to foreign invaders is an essential aspect of immunology which can be traced back directly to Galtsoff and Wilson’s work on sponges. The complex uses of sea sponges in biological research by Wilson, Galtsoff, Metchnikoff, and Huxley makes a case for the sponge’s entry into the pantheon of model organisms. This simple invertebrates’ versatility as a tool has allowed scientists like Wilson and Huxley to delve deeper to such a complex biological phenomenon.

Many other characteristics exemplify the sponge’s role as a model organism in the history of biology, outside of the larger historiographic gap and its versatility in both cell adhesion and immunological experiments. The sponge’s ubiquitous nature, as the center of many groundbreaking experiments in both early to late twentieth century, was due not only to its adaptability as an experimental subject but also due to the accessible manner in which the cells were acquired. In fact, Wilson had developed, in the same year that he published “On Some Phenomenon of Coalescence and Regeneration in Sponges”, a method to artificially rear sponges for future researchers to easily access the sponge, instead, having to rely on outside providers if one was not near a body of water, or having to go sponge diving as Wilson did on the USS Albatross. Wilson found that by obtaining sponges from the ocean, the organism slowly degenerated over time into plasmodial masses either singly or in groups. However, if the regenerative mass were placed in fine-bolting cloth bags and hung in a box floating on the harbor “freed as far as possible from any live oysters and crabs they could grow into functional sponges.”^[75] Over many periods of trial and error, Wilson found a method that proved to be quite successful.

The bags, rectangular, were divided into compartments about an inch square with the two flat sides nearly touching. In each such space, an isolated plasmodial mass was inserted, and the bag sewed up. It was found that in such bags the masses were held in place long enough for them to firmly attach to the bolting cloth. Once attached to the cloth they grow, sometimes quite through the wall to the outer water [inside the compartment] and transform into perfect sponges with an osculum, canals, pores and flagellated chambers in such abundance as to be crowded.^[76]

This method allowed Wilson to conduct his regenerative experiments without the added pressure of relying on outside providers or having to dive for sponges on the Beaufort Harbor. The newly created sponges were intact and functional enough for Wilson to reconstitute the sponges when excised from their containers. “If this is so, we have here a means of propagation which with a further development of methods may at some time be economically practical.”^[77] Beyond the apparent characteristics of economics and versatility, the most fundamental element of a model organism is its ^[78]standardization. The historian Dr. Rachel Ankeny summarized this best, stating that “the basic concept underlying model organism research is that certain species (or precisely strains of those species) which are relatively simple structurally and otherwise were standardized so that they could serve as resource materials in order to study particular biological phenomena exhaustively or in great detail including genetic and developmental processes”. In the same vein as other traditional organisms, that have passed this test to be labeled as a model organism, the sponge can also be a standardized organism in the early twentieth century. Since the 18th century, much of the zoological world was aware that sponges were simple creatures lacked the complexity of a nervous system, a cardiac system, and were composed of a simple digestive system and by the twentieth century many of their seemingly dynamic cellular structure and function were beginning to be teased out or, at the very least, well understood.  In its use as resource material, the paper has shown, quite convincingly, that sponges were being used exhaustively to study a variety of biological phenomena, such as biological individuality, regeneration, and immunology.

Discussion of Future Research

In the early to mid-twentieth century, there were several attempts by experimenters to discern the mode of communication between the individual sponge cells as they coalesced to form functional sponges. Both Wilson and Huxley had explained that the sponge cells communicated through haptic communication, in which organisms communicate or interact via touch. According to Huxley and Galtsoff’s research, the sponge cells’ protoplasm is the basis of this communication, as the cells’ touch and seem to understand which species they are and which differentiated cells they are as they combine to create a functional sponge. But, Galtsoff believed that sponge coalescence was possibly chemical in nature. This hypothesis is somewhat similar to the contemporary understanding of the slime mold, Dictyostelium discoideum. Dictyostelium is a peculiar slime mold, in that, if its parts are ever separated and in need of food, the individual slime molds produce a chemical response, cyclical AMP, or cAMP, which causes the slime mold amoeba to converge on the gradient of the chemical signal and form together as it is more beneficial to be a group than individual parts.^[79] Similarly, Galtsoff believed that sponge cells acted in the same way. However, after conducting a series of chemical assays to detect chemical responses from the cells, Galtsoff could not identify chemical signals from individual cells.^[80][81] Galtsoff eventually concluded that the sponge cells must undergo a process similar to a random walker scenario, in that the cells randomly combine, using an amoeboid movement to do as they attempt to group, as can be seen in Figure 5 below.  Figure 5 was a drawing of cell migration by Galtsoff in 1923. Galtsoff showed a particular sponge cell, the archaeocyte; of the Microciona genus making its way around the auger plate and as it traveled it was fusing with dermal cells, collar cells, and other archaeocyte cells to create an aggregate.^[82]

Figure 5. This drawing from Galtsoff’s 1923 article was of an archeocyte meandering around an auger plate, showing the reader a method of coalescence that doesn’t use chemical signaling but a sort of haptic communication.

Wilson, Huxley, and Galtsoff explanations for the recombination of individual sponge cells show that experimenters of the early to mid-twentieth century produced conflicting accounts of this remarkable phenomenon. There is now much contemporary historical and philosophical discussion of biological individuality. These scholarly discussions are, indeed, important as they offer new and exciting perspectives.  For example, a recent interpretation of biological individuality has come to light by a contemporary philosopher of biology, Andrew Reynolds. Reynolds focuses on cell communication, which was a fundamental aspect of both Wilson and Huxley’s experiments. This lens could be a promising focal point for scientists and philosophers as a way to understand the sponge’s ability to form distinct parts of a multicellular whole and how those parts can reform back into a functional sponge. However, this paper points out the need to review past experiments on sponge cells and their importance for examining the parts and the whole concept. By experimentally redesigning Wilson’s famed experiment, as well as its subsequent iterations by other biologists, in the contemporary sense, one may be able to discern the underlying aspects of how these individual sponge cells can determine self from non-self and regenerate and re-aggregate back into a functional sponge.^[83][84] Reworking Wilson’s experiment could, possibly, allow for experimental corroboration of Reynolds’ description of cell sociology as a way to understand the sponge’s ability to form distinct parts of a multicellular whole and then be able to reform back into a functional sponge. In fact, one promising focal point for scientists and philosophers of science-trained in laboratory science to hone in on would be a way to understand the sponge’s ability to form distinct parts of a whole and how those parts can reform back into a functional sponge after being incorporated as an aggregate of differentiated cells, as described in Figure 4.^[85][86] This phenomenon is known as sorting out, and it was a hotly debated topic of early twentieth-century regeneration research on sponges so much so, that Huxley attempted to tease out the internal mechanisms of the phenomenon in his 1912 essay on biological individuality. Huxley showed that the sponge cells seemed to know their function and place within the growing structure of what would eventually be a marine sponge.^[87] This phenomenon was not only noticed by Huxley but also by Wilson, who disregarded the idea of the internal set of cells sorting themselves out in favor of an alternative theory. He stated that archaeocytes, the most abundant cell type after dissociation, could differentiate into other cells as the sponge was reforming.^[88] Just as Reynolds noted, “cells are more than ‘building stones,’ but gregarious social organisms in constant communication with one another by either chemical or physical signals.”^[89] By repeating the initial experiment, one hopes to refine the notion of the parts and the whole concept, thereby determining how these individual parts can recombine to become a whole.

Conclusion

Haldane’s “suspicion is that the world is not only queerer than we suppose but queerer than we *can* suppose,” exemplifies the depth of knowledge cultivated from peering into and understanding the mechanisms of biology. The significance of this understanding during the 20^th Century was not lost on biologists, as many experiments transformed an originally philosophical and observational concept into a natural phenomenon. The work of Wilson and Huxley proved that the biological individual was more than just an organismal individual. It is an elaborate creation, consisting of levels of individuality that are more complex than previously thought.

This paper’s argument goes beyond analyzing a transition from the pre-twentieth century philosophical criterion of individuals to one of experimental legitimacy at the turn of the twentieth century. In the spirit of Lynn Nyhart’s 2017 work on biological individuality, entitled Biological Individuality: Integrating Scientific, Philosophical, and Historical Perspectives, the paper broadly integrates contemporary scientific methodology with historical and philosophical perspectives on the subject.  On one level the article provides a novel attempt to give experimental understanding to such a complex concept as biological individuality. It also highlights Wilson, a relatively obscure figure in the history of modern biology, and the sponge as a model organism, which has yet to make its mark among the pantheon of model organisms that have been dissected by contemporary historians of modern biology. Though, abilities of the sponge as a whole as well its cells has not escaped the eye of those contemporary biologists seeking to write histories of regeneration research or embryology. It is at the cellular and experimental level of biological individuality, which continues to fascinate philosophers and historians of biology. Wilson and Huxley’s preliminary experimental investigations enabled later scientists to examine further and refine notions of biological individuality and its importance.

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