page_title: History of Animals
section_title: Observations
hierarchical_section_title: History of Animals / Book / Observations
caption_attribution_description: English: Embryo of a chain catshark (Scyliorhinus retifer) removed from its egg case.
context_page_description: History of Animals is one of the major texts on biology by the ancient Greek philosopher Aristotle, who had studied at Plato's Academy in Athens. It was written in the fourth century BC; Aristotle died in 322 BC.
  Generally seen as a pioneering work of zoology, Aristotle frames his text by explaining that he is investigating the what prior to establishing the why. The book is thus an attempt to apply philosophy to part of the natural world. Throughout the work, Aristotle seeks to identify differences, both between individuals and between groups. A group is established when it is seen that all members have the same set of distinguishing features; for example, that all birds have feathers, wings, and beaks. This relationship between the birds and their features is recognized as a universal.
  The History of Animals contains many accurate eye-witness observations, in particular of the marine biology around the island of Lesbos, such as that the octopus had colour-changing abilities and a sperm-transferring tentacle, that the young of a dogfish grow inside their mother's body, or that the male of a river catfish guards the eggs after the female has left.
context_section_description: The History of Animals contains a large number of eye-witness observations, in particular of marine biology, in sharp contrast to Plato's "symbolic zoology". Aristotle's style and precision can be seen in the passage where he discusses the behaviour and anatomy of the cephalopods, mentioning the use of ink against predators, camouflage, and signalling. This is D'Arcy Thompson's translation:
  Of molluscs the sepia is the most cunning, and is the only species that employs its dark liquid for the sake of concealment as well as from fear: the octopus and calamary make the discharge solely from fear. These creatures never discharge the pigment in its entirety; and after a discharge the pigment accumulates again. The sepia, as has been said, often uses its colouring pigment for concealment; it shows itself in front of the pigment and then retreats back into it; it also hunts with its long tentacles not only little fishes, but oftentimes even mullets. The octopus is a stupid creature, for it will approach a man's hand if it be lowered in the water; but it is neat and thrifty in its habits: that is, it lays up stores in its nest, and, after eating up all that is eatable, it ejects the shells and sheaths of crabs and shell-fish, and the skeletons of little fishes. It seeks its prey by so changing its colour as to render it like the colour of the stones adjacent to it; it does so also when alarmed.
  — Historia Animalium IX.621b-622a
  His observations were almost all accurate, according to the philosopher Anthony Preus, though Mario Vegetti argues that Aristotle sometimes let theory cloud observation.
  Some of Aristotle's observations were not taken seriously by science until they were independently rediscovered in the 19th century. For example, he recorded that male octopuses have a hectocotylus, a tentacle which stores sperm and which can transfer it into the female's body; sometimes it snaps off during mating. The account was dismissed as fanciful until the French naturalist Georges Cuvier described it in his 1817 Le Règne Animal. Aristotle also noted that the young of the dogfish grow inside their mother's body attached by a cord to something like a placenta (a yolk sac). This was confirmed in 1842 by the German zoologist Johannes Peter Müller. Aristotle noted, too, that a river catfish which he called the glanis cares for its young, as the female leaves after giving birth; the male guards the eggs for forty or fifty days, chasing off small fish which threaten the eggs, and making a murmuring noise. The Swiss American zoologist Louis Agassiz found the account to be correct in 1890.
  Aristotle's methods of observation included dissection (Aristotle's lost companion work, The Dissections, contained illustrations of these), so he observed animal anatomy directly, though his interpretations of the functions of the structures he observed were subject to error. Like other classical authors such as Pliny the Elder, Aristotle also gathered evidence from travellers and people with specialised knowledge, such as fishermen and beekeepers, without much attempt to corroborate what they said.
caption: Aristotle recorded that the embryo of a dogfish was attached by a cord to a kind of placenta (the yolk sac).
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