Hertel 1 Aristotle’s Zoology: An Overview Animal Science in Time of Aristotle Megan Hertel Department of Classics, University of Florida Capstone Thesis 10 December 2019 Hertel 2 Abstract: In his many works on zoology, Aristotle makes detailed observations about the life histories, anatomies, and behaviors of a variety of organisms that inhabit a wide range. While his works are important for science, Aristotle’s findings contain inaccuracies due to the challenges posed by the technology of the time. Firstly, Aristotle recognizes the unique characteristics of invertebrates with high accuracy because they provide easy study specimens for his observations. Next, he writes about fish biology, particularly that of cartilaginous fish, and identifies the unique morphological features of this taxon. Further, while Aristotle fails to grasp their mechanism for respiration, he discovers that whales, dolphins, and seals breathe through lungs rather than gills. Additionally, Aristotle comes close to discovering how bees reproduce, yet misrepresents the reproduction of other insects. Also, he makes novel observations about reptiles and birds, especially in terms of their behavior. Lastly, Aristotle describes local and remote mammal species in detail, but he errs in regard to the biology of foreign megafauna because he likely did not see these animals in person. Aristotle’s contributions to biology and zoology continue to impact these fields today, even inspiring new scientific hypotheses. Despite the errors in his ideas, Aristotle’s writings influence the field of zoology and the whole of science by raising unique ideas and introducing observational and logical data collection. Hertel 3 In addition to his work on philosophy, Aristotle wrote a number of volumes on the biology, ecology, and anatomy of animals ranging from the sea sponge to the elephant. In these works, Aristotle attempts to explain natural phenomena based on observation and logic. Due to the nascent state of science when these books were written, much of Aristotle’s zoology contains fundamental errors. Despite this, Aristotle made surprising discoveries that were far before their time. First, Aristotle identifies aquatic invertebrates and explains their morphologies, but he makes mistakes regarding their reproductive biology. Furthermore, he understands the differences between bony fish and cartilaginous fish, as well as the difference between these groups and marine mammals. In contrast, Aristotle fails to understand how insects reproduce because of their high mobility and small size. Yet, he grasps biological concepts about reptiles despite the challenges that the organisms pose for data collection. Likewise, Aristotle’s zoological works make assessments of bird behavior that were not appreciated until modern times. Finally, Aristotle describes the mammalian megafauna of Europe and Asia with the help of external sources, which leads to errors in his theories. Aristotle’s zoology makes profound impacts on the scientists that followed him and gives modern readers an idea of the state of science in the ancient world. Aquatic Invertebrates: Fundamentally, Aristotle divides animals into two basic groups: ἔναιµα, those with blood, and ἂναιµα, those that do not have blood. Aristotle’s blooded animals include humans, reptiles, birds, fish, amphibians and mammals, while bloodless animals include insects, mollusks, echinoderms (sea urchins, sea stars, and their kin), and crustaceans (Parts of Animals, pp. 22). These divisions correspond with modern taxonomical classifications of vertebrate and invertebrate animals. Vertebrates are differentiated from invertebrates by the presence of a Hertel 4 notochord, a cartilaginous rod that supports the body of these organisms. Both of these taxa contain blood, though it comes in different forms in invertebrates; for example, the protein hemocyanin makes horseshoe crab blood blue, rather than the red blood that results from the presence of hemoglobin. In his works on zoology, Aristotle recognizes the differences between vertebrates and invertebrates without understanding what makes the two groups different. Outside of bloodless and blooded animals, Aristotle characterizes some animals as intermediate forms between two groups. One of these includes sponges, sea stars, and corals, all of which Aristotle considers intermediate between animals and plants (Parts of Animals, pp. 23). He does not consider these invertebrates as parts of his bloodless animals, but he does recognize the fact that they are living organisms and animals. Sponges are living, sessile organisms which can grow whole new sponges when they are cut into pieces (History of Animals, 548b6-7, 18- 19). As with the reproduction of other invertebrates, Aristotle is unclear about how sponges reproduce, since he says they are born spontaneously from crevices in rocks (History of Animals, 548a24-25). Sponges can reproduce asexually through fragmentation—like Aristotle describes— but also through sexual reproduction in broadcast spawning. Because two sponges do not have to come in contact or move to reproduce, Aristotle believes that sponges spontaneously appear without the assistance of other members of their species. Unlike in his discussion of sponges, Aristotle makes astute observations about sea urchins because they were easy for him to study. In Parts of Animals, he explains the internal and external anatomy of sea urchins, while only erring slightly. Aristotle delineates the motility of a sea urchin’s spines, its protective internal skeleton, and the five-rayed internal symmetry of a sea urchin’s prominent gonads (Parts of Animals, 679b26-30, 680b4-5). Additionally, he also describes their distinctive five-jawed feeding organ, comparing the structure’s shape to that of a Hertel 5 lantern (History of Animals, 530b24-25; 531a3-6). Today, the jaws of a sea urchin are known as Aristotle’s lantern due to this description. Furthermore, Aristotle correctly identifies the orientation of the sea urchin. He notes that they live oral-side down so that they can feed on benthic food sources (History of Animals, 530b19-23). This is an important discovery in understanding the feeding ecology and anatomy of a sea urchin; it also requires close observation, as their oral and aboral surfaces have only subtle differences. In general, Aristotle recognizes many of the characteristics that make sea urchins unique and that are vital to their taxonomic classification within the Phylum Echinodermata. On the other hand, Aristotle misunderstands the function of a sea urchin’s spines as he explains that they use their spines for locomotion (Parts of Animals, 681a7-9). Instead, sea urchins move using their water vascular system and tube feet, in which water pressure extends and retracts flexible projections from inside the urchin’s internal shell. Aristotle did not recognize the tube feet as the urchin’s means of movement because his specimens were primarily dead. He makes multiple references to dissecting sea urchins or harvesting them to eat, which would not permit him to see movement or tube feet without chemical preservation (Parts of Animals, 680a1-3; History of Animals, 530b16). Aristotle tends to have a greater volume of accurate knowledge about organisms to which he lives in close proximity, compared to foreign species. He understands the biology, anatomy, and ecology of sea urchins so well because they are common near him and accessible. Next, Aristotle categorizes octopuses, squids, and cuttlefish in their own group which he calls Malakia. In modern phylogenies, these same organisms belong to the Class Cephalopoda. These organisms are differentiated from other bloodless animals by their soft bodies that cover their hard parts, if they have any at all (History of Animals, 523b22). Aristotle observes that cuttlefish have a substantial but porous “bone,” squids have a thin and cartilaginous pen, and Hertel 6 octopuses have no internal, rigid support (History of Animals, 524b23-31). Because cephalopods belong to Phylum Mollusca, which also includes snails, oysters, and mussels, they secrete a shell. Unlike other mollusks, though, cephalopod shells are internal. Another difference among cephalopods is that in addition to the eight arms with two rows of suckers each that the octopus has around its mouth, squids and cuttlefish have two longer tentacles that they use to capture prey (History of Animals, 523b27-31). Also, octopuses have one arm that is bifurcated and used in copulation (History of Animals, 524a4-6). Aristotle refutes the theory of fishermen that the male octopus inserts this special tentacle into the siphon of the female in order to fertilize her eggs; rather, he suggests that this behavior connects the two together for some other method of copulation (Generation of Animals, 720b33-36). Contrary to Aristotle’s counter-hypothesis, many species of cephalopods use their hectocotylus, an arm specialized for reproduction, to transfer packets of sperm through the female’s siphon to her ovary. This behavior confused marine biologists for centuries; the hectocotylus gets its name from Georges Cuvier in the 19th century, who classified the detached arms of male octopuses he found in the siphon of females as a type of parasitic worm (Hardt 2016, pp. 126). Regardless of his errors in theory, Aristotle was able to observe the reproductive behavior of cephalopod mollusks without the assistance of modern technology. Aristotle presents his extensive knowledge on marine invertebrates throughout his zoological