In my last reading of the Categories I came across a curious line at
7a18, "Many animals, indeed, have no head." I wonder if it carries any weight as far as when Aristotle's biological interests began?
Edghill's translation (starting about 7a16) goes something like this:
A head will be more accurately defined as the correlative of that which is 'headed', than as that of an animal, for the animal does not have a head qua animal, since many animals have no head.
During that reading of the Categories I wrote in the margin, "Off the top of your head how many headless animals can you think of?--not many." Of terrestrial animals, I can think of worms, some insect larvae, but not many. The majority of headless animals probably belong to the marine invertebrates: all of the Coelenterates (corals, sea anemones), all Echinoderms (sea urchins, sea stars), some of the Mollusks (bivalves, not the cephalopods: octopus, squid, etc.)
I can imagine a marine biologist casually adding to some scientific discussion, "...of course, many animals do not have heads." But without an abiding biological interest I cannot imagine anyone making a statement like that, and especially in an off-hand manner in a non-biological treatise.
(I can picture a young Aristotle tossing that line out at a lecture and some of the stuffier members of the Academy looking at each other with questioning stares, "Did he just say, 'animals without heads?'")
The references to the location names in HA are often used to conclude that much of Aristotle's biological study began during the so-called middle period, later on in life, decades after the Categories is typically thought to have been written. I looked through the index locorum of Philosophical Issues in Aristotle's Biology and Cat 7a wasn't listed. It's probably too small a reference to make any kind of case for Aristotle starting his biological studies much earlier than is usually presumed. Still, I think an interesting remark.