NA TURE 



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THURSDAY, OCTOBER 27, i! 



THE STUDY OF EMBRYOLOGY. 

 Introduction to the Study of Embryology. By Prof. 

 [A. C. Haddon, M.A. (London : C Griffin and Co., 

 P887.) 



'HE publication of this volume supplies a long-felt 

 want. Many will remember the pleasure with 



lich the first appearance of an English volume solely 

 devoted to embryology was hailed. But there was a 

 good deal of the " lively anticipation of future favours " in 

 the gratitude with which the public received Part I. of the 

 " Embryology " by Foster and Balfour. The first edition 

 of this text-book contained, it will be remembered, a 

 clearly written, well illustrated account of what was then 

 known of the embryology of the chick. Although the 

 details were far in advance of anything previously pub- 

 lished on the subject in our language, yet the explanations 

 were so clear and the style so lucid that the book was in 

 every way suitable for the beginner. The public was 

 informed, in the introduction, that the work was to be 

 extended so that it would become a text-book of general 

 embryology. Although this promise was more than 

 fulfilled on the appearance of Balfour's classical work, 

 the young morphologist was to a certain extent the loser 

 by the immense benefit thus conferred upon the more 

 advanced student. The second edition of the former 

 book brought the account of the development of the 

 chick up to date, and a comparatively short description of 

 the essential features of embryological development in 

 Mammalia was added, but the work still remains an 

 enlarged Part I. But in the meantime the immense and 

 ever-increasing development of invertebrate embryology, 

 and the magnitude of the theoretical considerations raised 

 by its advance, rendered it more necessary than ever that 

 the beginner should be in possession of some introduc- 

 tion to this part of the subject ; and that the student 

 whom time and opportunity prevented from mastering 

 Balfour's great work should, nevertheless, be permitted 

 to gain some insight into the subject as a whole. 



Both these conditions are fulfilled, and corresponding 

 benefits will be conferred upon morphological teaching, by 

 the publication of Prof. H addon's text-book. In one re- 

 spect, indeed, it appears to be probable that the " Embryo- 

 logy" of Foster and Balfour will always remain pre-eminent 

 as a preliminary text-book for the young embryologist. 

 The limited scope of that work renders possible a 

 comparatively detailed description of the growth and 

 arrangement of the embryonic membranes and append- 

 ages, so that the relative positions of these to each other, 

 to the embryo, and to the yolk-sac, are brought before the 

 student with a clearness and force which could not be 

 attained in a more condensed statement. And the great 

 difficulty with which this part of the subject is grasped 

 by the beginner is apt to be undervalued by the advanced 

 student and by the teacher. Again, the selection of a 

 single type for detailed description renders possible and 

 indeed suggests that the succeeding stages of development 

 should be described after the manner of a diary ; and 

 while this method strongly impresses the imagination of 

 the reader, it gives continuity as well as reality to the 

 Vol. XXXVI. — No. 939. 



shifting scenes of embryonic development. It is also 

 probable that such a method, with its constantly repeated 

 recapitulations, and references to events which have been 

 previously described, must afford to the memory an 

 assistance which cannot be given by any other system. 

 Of course the full development of this method is totally 

 impracticable in a volume which deals with general 

 embryology, and the subject is not at present in a con- 

 dition such that it could be adequately represented by the 

 selection of a few types for detailed description. A book 

 which treats of the development of those mature organ- 

 isms which are usually selected as types of the 

 morphological series is much to be desired and would 

 be extremely useful, but in the present state of embryo- 

 logical knowledge it is doubtful whether such a volume 

 would represent general embryology as completely as 

 general morphology is represented by the types them- 

 selves. 



For the reasons given above, an ideal course of 

 embryology will begin wtth Foster and Balfour, continue 

 with Haddon, and end, as far as text-books are concerned, 

 with Balfour. The complete mastery in the first-named 

 work of a single easily accessible and readily investigated 

 type, of considerable complexity and difficulty, will enable 

 the student to grasp the shorter descriptions in Prof. 

 Haddon's volume of all important embryological dis- 

 coveries hitherto made. Finally, a rapid survey of general 

 embryology being thus gained, the student will pass to the 

 longer descriptions and further details of Balfour's classical 

 work. A course of embryological teaching so complete 

 as this, or so well suited to the needs of the student, does 

 not exist in any other language. 



It may be objected that in any such succession of text- 

 books there must be a great deal of waste, from the 

 description of the same developmental histories in rather 

 different language. For the advanced student or the 

 investigator the objection is valid, but I believe that every 

 experienced teacher will agree in the opinion that the 

 young student — for whom alone such a course is necessary 

 — gains immensely by this very fact, and learns far more 

 by reading a second text-book which puts the same 

 facts in a slightly different way, than by reading the first 

 text-book a second time. 



It is very high praise of Prof. Haddon's volume to place 

 it in the middle position of such a series. It is well and 

 clearly written, while the adoption of smaller type for 

 theoretical questions or less important details, is a great 

 benefit to the beginner. The figures are drawn so that 

 the primary layers and the organs derived from them can 

 be respectively tinted in uniform colours throughout the 

 book. While great additional clearness will be thus 

 conferred, the student will gain much during the process 

 of colouring. The illustrations are very numerous, and 

 although many of them are roughly executed, and open to 

 exception from an artistic point of view, their meaning is 

 sufficiently clear. In the vast preponderance of the re- 

 presentations of sections among the illustrations, the work 

 only follows the example of all books on the subject in 

 all languages, but it is to be doubted whether the course 

 of the young student is not somewhat impeded by this 

 universal custom. There is no doubt that, as Prof, 

 Weismann remarked to me the other day, the art of 

 section-cutting is a weapon for morphological research 



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