Aristotle's History of Animals In Ten Books · Aristotle
CHAPTER IX.
1. Among aquatic animals, there is one class of fish, which embraces many forms, and is separated from other animals, for it has a head, and upper and lower parts, in which last are the stomach and bowels, and a continuous and undivided tail. This is not alike in all. They have neither neck nor limb, nor internal and external testicles, nor mammæ, nor has any other animal mammæ that is not viviparous, nor indeed all viviparous animals, but those only that are internally viviparous, and not first of all oviparous. For the dolphin is a viviparous animal, wherefore it has two mammæ, not indeed above, but near the organs of reproduction. It has not evident nipples, but, as it were, a stream flowing from each side. From these the milk exudes, and the young ones suck as they follow the mother. This has been distinctly observed by some persons. 2. But fish, as we have observed, have neither mammæ nor any external passage for the genital organs. In the branchia they have a distinctive organ, through which they eject the water they have received into their mouths; and they have fins, most fishes have four, but the long fishes, as the eel, have only two placed near the branchia, and in this respect the cestreus,[40] a fish in the lake of Siphæ, is similar to the eel,[41] and so is the fish called tænia.[42] Some of these long fish have no fins, as the muræna, nor have they divided branchia like other fish.
Text from Project Gutenberg, public domain in the United States.