BOOK IV.--Animals without blood, and first, the cephalopods, are described; then the crustaceans, testacea, echinidæ, ascidians, actiniæ, hermit crabs, insects. In the eighth chapter the organs of sense are considered, and afterwards, the voice, sleep, age, and differences of the sexes in animals are described. BOOK V.--In the former books animals are for the most part described with reference to their several parts. In the fifth book they are treated as entire, and especially with regard to their mode of reproduction. First of all, our author treats of spontaneous reproduction, and then of those animals which spring from a union of the sexes; and from this he proceeds to some detail with respect to different groups of animals, testacea, crustacea, insects. The book concludes with a long description of bees and their habits. BOOK VI.--In this book the same subject is continued through the several classes of birds, fish, and quadrupeds. This account of the reproduction of animals includes also the consideration of the seasons, climates, and ages of animals, and how far these influence their reproduction. BOOK VII.--The seventh book is almost entirely devoted to the consideration of the reproduction of man, and an account of man from his birth to his death. This book ends abruptly, and is probably imperfect. BOOK VIII.--In the eighth book Aristotle passes on to the most interesting part of his work, the character and habits of the whole animal world, as it was known to him. The amount of detail which he has collected and arranged on this subject is most interesting. He treats, first of all, of the food of animals, of their migrations, their health and diseases, and the influence of climate upon them. BOOK IX.--The subject of the eighth book is continued, with an account of the relations in which animals stand to each other, and especially the friendship and hostility of different species; and these are for the most part referred to the nature of their food, and their mode of procuring it. The notices of fish are not so numerous as those of other groups: this would necessarily arise from the difficulty of observation. At the conclusion of the book, an essay on bees and their congeners is given at considerable length. BOOK X.--This book, in all probability erroneously ascribed to Aristotle, is occupied with a treatise on the causes of barrenness in the human species. It appears to be rather a continuation of the seventh book, which ends abruptly; but it is well placed at the end, as no genuine work of our author. THE HISTORY OF ANIMALS. BOOK THE FIRST. CHAPTER I.