NATURE 



60 1 



THURSDAY, OCTOBER 28, 18S0 



BALFOUR'S "COMPARATIVE EMBRYOLOGY" 



A Treatise on Comparalivc Embryology. By Francis M. 



Balfour, M.A., F.R.S., Fellow and Lecturer of Trinity 



College, Cambridge. In Two Volumes. Vol. I. 



(London : Macmillan and Co., iSSo.) 



IT is scarcely possible to exaggerate the expressions of 

 gratitude which are due from zoologists to i\Ir. Balfour 

 for the execution of the great task which some three or 

 four years ago he set himself. Zoologists have to be 

 thankful to him not only for the admirable style in which 

 he has carried out his work, but for the promptitude with 

 which he has achieved it. Mr. Balfour's object was to 

 produce a work in Avhich all that has been written during 

 the last ten or fifteen years on the structural features 

 exhibited by animals during their growth from the egg to 

 the adult condition should be digested, and its import 

 carefully estimated ; the result being set forth in a syste- 

 matic way, so that the broad conclusions arrived at by 

 the almost innumerable studies of " development from 

 the egg" in all sorts and conditions of animals should be 

 pointedly placed before the reader. At the same time 

 he aimed to provide for the purpose of reference and for 

 the guidance of future students something like a complete 

 bibliography, accompanied by an analysis in many cases, 

 of the works which have been published on special forms. 



It is very well known to those who are in a position to 

 make a comparative estimate, that during the last fifteen 

 years in no branch of science has there been such activity, 

 such abundance of discovery, of careful obsen-ation and 

 ingenious speculation, as in biology ; and this activity has 

 tended more and more to concentrate itself upon the 

 study of the mode in which the complex adult organism 

 (whether plant or animal), with all its astounding powers 

 and its beauty of form — slowly, surely, and yet by most 

 improbable and devious ways, advances to its complete 

 estate from the condition of a microscopic structureless 

 globule of albuminous slime. This marvel of develop- 

 ment is one which has only recently come to man's know- 

 ledge, and it seems likely that the fascination which the 

 study of it can exert will be such as to attract the 

 energies of an ever-increasing crowd of observers. 



Mr. Balfour's book gives for those who are to come a 

 rt'sitme or summing up of the labours of those who have 

 up to this date worked for and created our knowledge of 

 what this process of growth from the egg is and signifies. 



The first volume deals with the history of development 

 in all groups of animals excepting the \'ertebrata. The 

 labour which it has involved will be understood when it 

 is stated that the author gives references to five hundred 

 and se\-enty-two separate memoirs or books, most of 

 which he has thoroughly read, and from many of which 

 he gives extracts or carefully condensed abstracts. 



The thoroughness with which the subject is presented 

 to the student may be appreciated by a consideration of 

 the fact that two hundred and seventy-five woodcuts are 

 given in this volume, which are, with few exceptions, 

 prepared especially for this work, either from the author's 

 original drawings or from the drawings of the writers 

 whom he is summarising. 

 Vai-. XXII.— No. 574 



The work is divided into an "Introduction" and a 

 " Systematic Embryology." In the Introduction we have 

 chapters on "The Ovum and the Spermatozoon," on 

 "The Maturation and the Impregnation of the Ovum," 

 and on " The Segmentation of the Ovum." The syste- 

 matic portion is divided into chapters, each of which 

 corresponds with one of the large divisions of animals, 

 e.g. Porifera, Platyelminthes, Rotifera, MoUusca, Chaeto- 

 poda, &c. 



Mr. Balfour, it is hardly necessary to sa)-, has not per- 

 formed his task as an ordinary maker ofbooks. He 's, as 

 all zoologists know, one of the foremost students of em- 

 bryology in Europe, and has added a very large propc 

 tion himself to that great heap of isolated embryological 

 memoirs and monographs which it is the purpose of his 

 book to condense and render accessible to a wider circle 

 of students. Consequently we find not only new and 

 original observations scattered here and there in the 

 chapters of this treatise, but on the very numerous 

 matters which call for the expression of an opinion or 

 the exercise of judgment between conflicting statements 

 of preceding observers, we have the conclusions, always 

 modestly formulated, of a thoroughly competent critic. 



In fact those who are already advanced in the study 

 of embryology will find that Mr. Balfour has freely and 

 most legitimately made use of speculative views of his 

 own, as a series of strings on which to thread the almost 

 innumerable observed facts which ha\-e to be put on 

 record and kept ready, as it were, for the future building 

 up of embryological doctrine. The reader, on the other 

 hand, who has not yet reached the degree of knowledge 

 at which such speculations become intelhgible, will find 

 that there is so much in Mr. Balfour's pages of hard, 

 solid, descriptive record of the actual developmental 

 changes of one animal after another, that he will certainly 

 not feel cause to complain. 



It would be out of place to discuss in these pages 

 any of the new theoretical considerations which Mr. 

 Balfour puts forward. With some of them it is possible 

 to find fault ; at the same time they are all ingeniously 

 supported and indicate close reasoning and a large survey 

 of facts on the author's part. They serve, as Mr. Balfour 

 himself recognises, to stimulate inquiry, and when advanced 

 not by a paper-philosopher, but by a most exceptionally 

 industrious observer, they cannot fail to command respect. 



If we venture to offer any remark which suggests how 

 possibly Mr. Balfour's book might have been even more 

 excellent than it is, it must be clearly understood that 

 as it stands we hold it to be a perfect mine of valuable 

 information and well-considered suggestion. We should, 

 however, have been glad had it been possible for the 

 author to give more attention to the history of the various 

 stages of progress in our knowledge of embryology in 

 general, and of each particular group. Full justice is done 

 to recent authors, and his own contemporaries receive 

 ample recognition from Mr. Balfour ; but the successive 

 steps by which a particular point of view has been arrived 

 at are not always definitely indicated and due merit 

 assigned to each of those who in past times has laboured 

 to bring about the present phase of science. This, no 

 doubt, has not entered into Mr. Balfour's plan on account 

 of the additional responsibility and labour which it would 

 have involved, and the increase in size of what is already 



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