In his second book, he treats more particularly of animals. At its commencement we unfortunately meet with a stumbling-block, in the shape of an assertion, that the neck of the lion has no vertebræ, but consists of a single bone. In speaking of limbs, he takes occasion to describe the proboscis of the elephant, and to enter generally into the history of that gigantic quadruped. He then speaks with reference to the distribution of hair, remarking, that the hair of the human head is longer than that of any other animal; that some are covered all over with long hair, as the bear; others on the neck only, as the lion; and others only along the back of the neck, as the horse and the bonasus. He describes the buffalo and the camel; of the latter of which he mentions the two species, the Arabian and the Bactrian. The subject of claws, hoofs, and horns, is next discussed. He states that some quadrupeds have many toes, as the lion; while others have the foot divided into two, as the sheep; and others again have a single toe or hoof, as the horse. His aphorisms on the subject of horns are in general correct. Thus, he states that most creatures furnished with them have cloven hoofs, and that no single-hoofed animal has two horns.
He then proceeds to speak of teeth, which he says are possessed by all viviparous quadrupeds. Some have them in both jaws, others not; for horned animals have teeth in the lower jaw only, the front ones being wanting in the upper. Yet all animals which have no teeth above are not horned; the camel, for example. Some have projecting teeth, as the boar; others not. In some they are jagged, as in the lion, panther, and dog; in others even, as in the horse and cow. No animal has horns and protruded teeth; nor is there any having jagged teeth that has either horns or projecting teeth. The greater part have the front teeth sharp, and those behind broad; but the seal has them all jagged for it partakes of the nature of fishes, which have that peculiarity. His remarks on the shedding of the teeth are in general erroneous. The elephant, he says, has four grinders, together with two others, the latter of which are of great size and bent upwards in the male, but small and directed the contrary way in the female. This circumstance Cuvier states to be correct with respect to the African variety, although the case is different in the Asiatic. His account of the hippopotamus, however, is inaccurate in almost every particular. Thus, he says it has a mane like a horse, cloven feet like an ox, and is of the size of an ass,—a description which answers better to the gnu. In speaking of monkeys, of which he mentions several kinds, he remarks their resemblance to the human species, and the peculiar formation of their hind feet, which may be used as hands.
He then gives a general account of the oviparous quadrupeds, particularly of the Egyptian crocodile and the chameleon, concerning which he relates many interesting circumstances.
In treating of birds, he remarks that they are bipedal, like man, destitute of anterior limbs, but furnished with wings, and having a peculiar formation in the legs. Those birds which have hooked claws, he says, have the breast more robust than others. He then describes the differences in the structure of their feet; remarking, that most of them have three toes before and one behind, although a few, as the wryneck, have two only before. Birds, he adds, have the place of lips and teeth supplied by a bill; and instead of external ears and nostrils properly so called, they have passages for hearing and smelling in different parts of the head. The eyes have no lashes, but are furnished with a membrane like lizards. The other remarkable peculiarities, such as the feathers and the form of the tongue, are then mentioned. No birds, he observes, that have hooked claws are furnished with spurs. In his remarks on this family he is generally correct; though here, as elsewhere, he is not merely brief, but vague and superficial. His division of birds would seem to be the following:—Those with hooked claws; those with separated toes; and such as are web-footed.
Fishes are next discussed with nearly equal brevity. He remarks, that they have a peculiar elongated form, are destitute of mammæ, emit by their gills the water received at the mouth, swim by means of fins, are generally covered with scales, and are destitute of the organs of hearing and smelling.
His description of the internal parts of these tribes of animals contains a mixture of truth and error. This book terminates with remarks on the structure of serpents.
The third commences with observations on those parts of animals which are homogeneous, such as the blood, the fibres, the veins, the nerves, and the hair. Under the general title of nerve, he confounds the columnæ carneæ of the heart, the tendons and fasciæ; and it does not appear that he had any idea of what modern anatomists call nerves. In speaking of hair, he remarks that it grows in sick persons, especially those labouring under consumption, in old people, and even in dead bodies. The same remark applies to the nails. The blood is contained in the veins and heart, is, like the brain, insensible, flows from a wound in any part of the flesh, has a sweet taste and a red colour, coagulates in the air, palpitates in the veins, and when vitiated is productive of disease. On the subject of milk, his observations deserve attention. Thus, he says that all viviparous animals which have hair are furnished with mammæ, as are also the whale and the dolphin; but those which are oviparous are not so provided. All milk has a watery fluid, called serum, and a thick part, called cheese; while that produced by animals which are destitute of fore teeth in the upper jaw coagulates. On this subject he mentions some curious circumstances. Some kinds of food occasion the appearance of a little milk in women who are not pregnant. There have even been instances of it flowing from the breasts of elderly females. The shepherds about Mount Œta rub the udders of unimpregnated goats with nettles, and thus obtain abundance of milk from them. It sometimes happens that male animals secrete the same fluid; thus, there was a he-goat in the island of Lemnos, which yielded so much that small cheeses were made of it. A little may be pressed from the breasts of some men after the age of puberty; and there have been individuals who on being sucked have yielded a large quantity. Instances of this have been recorded by other observers; and Humboldt met with a similar case in South America.[D]
In the fourth book, Aristotle treats of the animals which are destitute of red blood. Of these, he says there are several genera: the mollusca, such as the cuttlefish, which is externally soft with an internal firm part; the crustacea, internally soft and covered with a firm integument, such as the crab; the testacea, internally soft and externally hard and solid, as the limpet and oyster. The insects form the fourth genus; and are distinguished by their being externally and internally formed of a hardish or cartilaginous substance, and divided into segments; some of them having wings, as the wasp; while others have none, as the centipede. He then gives a pretty full account of the cuttlefish and nautilus, treats of the crustaceous animals generally, and enters into details respecting the other two classes. After this he enumerates the organs of sensation, stating that man, and all the red-blooded and viviparous animals, possess five senses, although in the mole vision is deficient. He describes correctly the eye of that creature, showing that it is covered by a thickish skin, but presents a conformation similar to that of other animals, and is furnished with a nerve from the brain. He shows that although fishes have no visible organs of smelling or hearing, they yet possess both senses, and, in treating of this subject, states many interesting facts relative to the mode employed in catching dolphins. He also shows that insects have the faculty of hearing and smelling. The testacea, he says, besides feeling, which is common to all animals, have smell and taste; but he also asserts that some of them, the solen and pecten, are capable of seeing, and others of hearing.
All viviparous quadrupeds not only sleep, but also dream; but whether the oviparous dream is uncertain; although it is plain that they sleep, as do the aquatic animals, fishes, mollusca, testacea, and crustacea. A transition is then made to the subject of sex, for the purpose of showing that in the mollusca, crustacea, testacea, and eels, there is no difference in that respect between individuals of the same species.
The subjects of generation and parturition occupy the fifth, sixth, and seventh books. From the comparatively large space which he has devoted to the result of his inquiries in these departments, the minuteness with which he describes the phenomena presented by them in man and the domestic animals, and the accurate knowledge which he frequently exhibits, it may be inferred that they were favourite subjects with Aristotle. It is sufficient for our purpose to mention some of the cases in which he attained the truth, and others in which he failed.