The present edition of 'Forms of Animal Life' was taken in hand by the late Professor Rolleston in the Long Vacation of 1879. The work was carried on with prolonged interruptions, incident to a life of many and varied engagements, until he left England in December 1880. By that time he had completed the descriptions of Preparations 1-9; three new Plates (Pls. IV, VII, IX) had been engraved under his direction, and he had compiled notes upon them, which have been employed in the descriptions printed in this volume.

Soon after beginning his work, the Professor asked me to undertake a joint authorship of the book. The part then assigned to me was to rewrite the descriptions of a certain number of the Preparations, the general accounts of Urochorda, Arthropoda, parasitic Vermes, Coelenterata and Protozoa, as well as of several minor classes. He read my account of Protozoa, and settled that it should form a model for the accounts of all other groups. As now printed it has been so far modified as to accord with the recent progress of knowledge.

When Professor Rolleston went abroad he put me in possession of his plans for the rest of the work, handed his papers to me, and expressed a hope that, if he were disabled from completing the new edition, I might be the person to do it in his stead. It is almost needless for me to add that in fulfilling this sacred trust I have endeavoured to carry out his wishes, which were mainly three: (1) to enlarge the descriptions of the Preparations and accounts of the various classes of animals, and bring them to the standard of contemporary knowledge; (2) to add to each class or group a brief classification; and (3) to give as full a bibliography as space would permit.

The method I have adopted to meet the last requisition is to cite the most important and recent authorities which, when consulted, will in most cases give the names of all other accounts worth reading, so as to form a really very complete index to the state of present knowledge. These authorities write chiefly in foreign languages, and I need scarcely remark that every modern anatomist must also be a modern linguist. Literature, though not everything in Science, is yet indispensable, and as Professor Rolleston observed in the preface to the first edition of his book (pp. viii-ix): 'In some cases even the beginner will find it necessary to consult some of the many works referred to in the descriptions of the Preparations and in the descriptions of the Plates; but the bibliographical references have been added with a view rather to the wants indicated in the words "Fur Akademische Vorlesungen und zum Selbststudium," so often prefixed to German works on Science, than to those of the commencing student'

The debateable points of Phylogeny are not treated at any length. Professor Rolleston, having tried one experiment, particularly desired that they should be omitted on account of the great space their adequate discussion must needs occupy.

One alteration in the arrangement of the volume had been contemplated by the Professor, but left unsettled, and has now been carried out in consequence of the opinion of Professor Huxley in its favour. The descriptions of the Preparations, those of the Plates, and the general account of the Animal Kingdom, have changed places. The two former stood last in the first edition, but take precedence in this. The new arrangement tallies better with the order in which Professor Rolleston wished the several parts to be studied, as stated, loc. cit. pp. vii-viii: 'It is recommended that in all cases the study of the described Preparation or specimen should precede that of the accounts in the Introduction (i. e. General account of the Animal Kingdom, Ed.) of the Class and Sub-kingdom (i.e. Phylum, Ed.) to which it belongs, and that the study of the Plates should be taken up only after the attainment of a considerable familiarity with actual specimens by the practice of dissection.'

The Plates, however, illustrate the Preparations, and are therefore placed as the second section of the book 1.

1 A few changes in the Preparations have been made. Some have been added, e. g. those relating to the Rabbit; the Privet Hawk Moth has been substituted for the Death's Head which is difficult to procure; similarly, the Dog's Tapeworm and its Cysticercus replace the Bladderworm of the Sheep (Coenurus). The skeleton of the Common Fowl, two dissections of a Caterpillar, the angular Sea Cucumber, and the Bugle Coralline, have been omitted. The Preparations were made by Charles Robertson, Esq., Demonstrator of Anatomy in the University Museum; the greater part although the Professor contemplated the above-mentioned changes, he desired to retain the 'distinctive character' of the book. This character, as he himself said, loc. cit. pp. v-vi : 'Consists in its attempting so to combine the concrete facts of Zootomy with the outlines of systematic Classification as to enable the student to put them for himself into their natural relations of foundation and superstructure. The foundation may be made wider, and the superstructure may have its outlines not only filled up, but even considerably altered by subsequent and more extensive labours; but the mutual relations of the one as foundation, and of the other as superstructure, which this book particularly aims at illustrating, must always remain the same.'

Another observation may be quoted, loc. cit. p. vi: 'It is hoped that this work, though written with a view chiefly to the needs of University students of Comparative Anatomy, and with special reference to the application of that branch of science as an engine of instruction, may in some measure meet the requirements of the now not inconsiderable number of persons who are attracted to the study by seeing the important bearings which it has upon questions not only of theoretical and philosophical, but also of practical interest.'

It would have been more agreeable to my own feelings if this second edition had been issued at an earlier date. But the great length of time which has elapsed since the publication of the first - full seventeen years - has brought with it so many and such vast changes in Comparative Anatomy that great labour and consequent delay became inevitable. I may mention that scientific periodicals on the general subject and its branches have since 1870 been almost doubled, not only in number, but also in bulk; and one whole science - that of Comparative Embryology - has been formulated and now constitutes the foundation of all Anatomy. Any worker placed single-handed under such conditions, is at a great disadvantage even with all the modern paraphernalia of abstracts. And I have to add a lesson learnt by personal experience, that in most cases the best abstract available cannot by any means stand in the place of the original paper. Among other causes of delay my own employment as a teacher must be taken into account, and there have also occurred of them were exhibited by him as a ' Zoological series with Dissections in illustration,' in the Educational Department of the Great Exhibition of 1862.

Thirteen woodcuts have been added in the text, and three new Plates (Pis. IV, VII, IX). Of the old plates, one (PI. IX of the first edition) has been cancelled. The woodcuts I-5 and the three new plates have been drawn by Julian Drummond, Esq., the present Radcliffe Artist; the plates of the first edition were drawn by his predecessor, George Crozier, Esq. many unforeseen interruptions. Under these circumstances it is my pleasant duty to thank the Delegates of the University Press for their kind forbearance on the question of time.

My warmest thanks are due to Sir H. W. Acland, K.C.B., F.R.S., for the use of a room belonging to his own suite in the University Museum, and for a free and extensive command of all requisite literature in that rich storehouse of scientific books, the Radcliffe Library, without which my task could never have been accomplished. To Professor Moseley, F.R.S., Dr. Rolleston's successor in the Linacre chair, I render my best thanks for an unlimited employment of the anatomical collections under his charge, and the loan of his own MS. notes on the Anthozoa Zoantharia. I have also to record a debt of gratitude to my early and constant friend, Professor Westwood, who has given me much assistance by way of access to specimens and pamphlets on the difficult phylum Arthropoda. In kind compliance with my request, Professor Ray Lankester, F.R.S., liberally allowed me to copy two figures of his own construction (Woodcut 13, A, B, and 1, 2, 3,4); and Professor Kitchin Parker, F.R.S., furnished valuable information, at the time unpublished, relative to points in the development of the Vertebrate skull, and also granted permission for the use of two figures (Woodcuts, 6 and 7) illustrating the skull of the common Frog. I have to thank Mr. C. Robertson, who was conversant with Professor Rolleston's wishes, for assistance on various points, and Mr. G. C. Bourne for several suggestions and for other help; nor must I by any means omit Professor W. B. Spencer of Melbourne University, and Mr. G. H. Fowler, to whose most timely and friendly care I am entirely indebted for the addition of the Index.

The compilation of this book, though laborious in the extreme, has been attended by its pleasures. But the crowning pleasure of all can only befall me if its publication gains the sympathy of those who are competent to judge the nature of the task, and the book itself proves a real aid to students in this most fascinating science of Comparative Anatomy.

Wm. Hatchett Jackson.

Museum, Oxford :

September 24, 1887.