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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[Pg 68] 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[Pg 69] 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;[Pg 70] 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.

He describes the membranes with which some of the mollusca envelope their eggs, mentions the changes through which insects pass before they acquire the perfect state, and speaks with tolerable accuracy of the economy of bees and wasps. He states, however, that the former make wax from flowers, but gather their honey from a substance which falls from the air upon trees. The eggs of tortoises, he says, are hard, like those of birds, and are deposited in the ground. His remarks on those of lizards and the crocodile are also correct. He states accurately that some serpents bring forth their young enclosed in a soft membrane, which they afterwards burst; but that sometimes the little animals escape from the egg internally, and are produced free. Other serpents, he observes, bring forth eggs cohering in the[Pg 71] form of a necklace. On the eggs of birds his observations are nearly as correct as those which we find in books at the present day. He was acquainted with their general structure, and the development of the chick, which he minutely describes. He remarks of the cuckoo, that it is not a changed hawk, as some have asserted; that, although certain persons have alleged that its young have never been seen, it yet certainly has young; that, however, it does not construct a nest, but deposites its eggs in the nest of other birds, after eating those which it finds there.

He remarks that the cartilaginous fishes are viviparous, but that the other species bring forth eggs, and states correctly that they have no alantoid membrane. He then passes to the cetacea, with which he seems to be nearly as well acquainted as modern naturalists, and reverts to the oviparous fishes, respecting which he presents numerous details. He maintains, however, that the eel is produced spontaneously, and that no person had ever detected eggs or milt in it.

Having discussed the subject of generation, he proceeds, in the eighth book, to treat of the food and actions of animals, their migrations, and other circumstances. The ninth consists of a multitude of topics without any direct relation to each other, but apparently treated as they had successively presented themselves to the author. Thus, at the commencement we find remarks on the peculiarities of disposition observed in the males and females of different animals, the combats of hostile species, the actions of animals, nidification, generation, and other matters. Several species of different classes[Pg 72] are then described, such as the kingfisher, the black-bird, the cuckoo, the marten, eagles, owls, fishes, insects, and quadrupeds.