That the thorough study of concrete animal types is a necessary preliminary to good work in Zoology or Comparative Anatomy will now be granted by all competent judges. At a time when these subjects, though much lectured upon, were rarely taught, DÖllinger, of WÜrzburg, found out the right way. He took young students, often singly, and made them master such animal types as came to hand, thereby teaching them how to work for themselves, and fixing in their minds a nucleus of real knowledge, around which more might crystallise. “What do you want lectures for? Bring any animal and dissect it here,” said he to Baer, then a young doctor longing to work at Comparative Anatomy.1 It was DÖllinger who trained Purkinje, Pander, Baer, and Agassiz, and such fame cannot be heightened by words of praise. In our own time and country DÖllinger’s methods have been practised by Professor Huxley, whose descriptive guides, such as the Elementary Biology and the delightful little book on the Crayfish, now make it easy for every teacher to work on the same lines. From the description of the Cockroach in Huxley’s Anatomy of Invertebrated Animals came the impulse which has encouraged us to treat that type at length. It may easily turn out that in adding some facts and a great many words to his account, we have diluted what was valuable for its concentration. But there are students—those, namely, who intend to give serious attention to Entomology—who will find our explanations deficient rather than excessive in detail. It is our belief and hope that naturalists will some day recoil from their extravagant love of words and names, and turn to structure, development, life-history, and other aspects of the animal world which have points of contact with the life of man. We have written for such as desire to study Insects on this side.

Whoever attempts to tell all that is important about a very common animal will feel his dependence upon other workers. Much of what is here printed has been told before. The large number of new figures is, however, some proof that we have worked for ourselves.

It is a pleasant duty to offer our thanks for friendly help received. Professor FÉlix Plateau, of Ghent; Mr. Joseph Nusbaum, of Warsaw; and Mr. S.H. Scudder, of Cambridge, Massachusetts, have very kindly consented to treat here of those parts of the subject which they have specially illustrated by their own labours.2 Mr. E.T. Newton, of the Jermyn Street Museum, has lent us the wood blocks used to illustrate one of his papers on the Brain of the Cockroach. A number of the figures have been very carefully and faithfully drawn for us by Miss Beatrice Boyle, a student in the Yorkshire College. We are much indebted to Dr. Murie, the Librarian of the Linnean Society, for procuring us access to the extensive literature of Insect Anatomy, and for answering not a few troublesome questions.

Five articles on the Cockroach were contributed by us to Science Gossip in 1884, and some of the figures were then engraved and published.

In issuing a book which has been long in hand, but which can never hope to be complete, we venture to adopt the words already used by Leydig concerning his Lehrbuch der Histologie:—“Die eigentlich nie fertig wird, die man aber fÜr fertig erklÄren muss, wenn man nach Zeit und UmstÄnden das MÖglichste gethan hat.”