NA TURE 



271 



THURSDAY, MAY 6, 1909. 



VERTEBRATE DEVELOPMENT. 

 The Development of the Chick. An Introduction to 

 Embrj'ology. By F. R. Lillie. Pp. xi+472. (New 

 York : H. Holt and Co. ; London : G. Bell and 

 Sons.) Price 16s. net. 



THE first feeling of an embryologist on examining 

 this beautiful volume is of disappointment and 

 regret that it treats solely of the development of so 

 familiar an animal as the chick. The like style of 

 work, dealing with some less-known form, might 

 have been a very valuable original monograph. The 

 chick has, indeed, played a very large and undeserved 

 part in the history of embryology from the time of 

 Harvey, Caspar Friedrich Wolff, and earlier, through 

 all the years during which Pander and Carl Erhst von 

 Baer devoted themselves to its study, down to to-day. 

 The incubator of the embryological laboratory is a 

 silent witness of the importance often still attached 

 to the development of the common fowl in the teach- 

 ing of embryology. In addition to the employment 

 of this animal in the laboratory, mafiy embrVologists 

 have found the incubated egg of the hen useful, at 

 times invaluable, in their researches. None the less, 

 like the type-system of the zoological laboratory, the 

 chick has seen better days in embryological work 

 and teaching. Convenience has become the sole 

 reason for its continued employment. For most, if 

 not all, of the subjects of a course of embryology it 

 is not difficult at all to find far more suitable material 

 for instruction. 



No embr\'o!ogist would think of attempting to 

 demonstrate the wonderful story of the germ-cells, 

 the phenomena of the maturation of germ-cells, 

 fertilisation, egg-cleavage, or even of the formation 

 of the so-called germinal layers with material sup- 

 plied by the development of the chick. In almost 

 every field of embryological research, where funda- 

 mental questions have been solved or brought nearer 

 solution, material from other animals has been em- 

 ployed. " The book is meant for beginners in em- 

 bryology," we are told in the preface, and the long 

 list of literature at its close is intended doubtless 

 as a further guide to him. It embraces, however, 

 only those memoirs in which the developmental 

 features of the highly specialised bird find a place. 

 The beginner, therefore, having worked through the 

 boolj and some or all of the literature, will have 

 gained a very erroneous idea of what modern em- 

 bryology really is. Most of the important parts of 

 its literature on all sorts of questions will not have 

 been brought to his notice. For example, the classic 

 memoirs of Boveri and F. Meves on oogenesis and 

 spermatogenesis, those of Mark, Whitman, and E. B. 

 Wilson on egg-cleavage, or of E. van Beneden, 

 Hubrecht, and Duval on the trophoblast and placenta, 

 can of necessity find no place or mention in a work 

 designed as this has been. After a close study of 

 the work, the student may not unnaturally put a 

 question we have often heard, " What is trophoblast ? 

 Is it a name invented for something existing onlv in 

 NO. 2062, VOL. 80] 



the imagination of some ' versatile ' embryologist? " 

 What a revelation would it not, then, be to him to 

 read Hubrecht's classic monograph on the tropho- 

 blast and placentation of the hedgehog (1889"*, to 

 be followed by the study of the works of Duval, E. 

 van Beneden, and J. P. Hill ! 



Were one, indeed, to search for the cause of the 

 existence and persistence of so much that is erroneous 

 in embrvology, the convenient chick would probably 

 be found to be the chief culprit. Of what value is 

 it to the student to learn that the thymus arises from 

 the walls of the third and fourth branchial pouches, if 

 at the same time he remain ignorant that such a 

 restricted origin be not by any means universal, and 

 that there be fishes in which each and every branchial 

 pouch may furnish its thymus element? The nature 

 of the thymus could never be solved from its develop- 

 ment in the chick. The mode of development of 

 important structures from well-defined placodes or 

 plates of cells, each placode probably having a first 

 origin in a single cell, cannot be demonstrated from 

 the embryology of the chick. 



This animal has always been, and it still is, the 

 bulwark of the doctrine of epigenesis, and tTiis 

 because the true developmental phenomena are often 

 here obscure. The placodes of piscine development 

 lead us in the direction of the large single cells or 

 teloblasts of the earthworm, and the two things have 

 significant bearings on the question of the mode of 

 the development, whether by epigenesis, as Wolff 

 and most other embryologists have thought, or by 

 evolution with pre-determination, not pre-formaiion. 

 as some embryologists are beginning to suspect. 



What the beginner requires, we imagine, is not 

 so much facts as principles, those underlying the 

 development. Unless it be the formation of the 

 germinal layers, and concerning the truth of the 

 germ-layer theory sceptics are not wanting, it is diflficult 

 to say what embryological principle can be illus- 

 trated from the developmental pictures presented by 

 this animal. Direct development or alternation of 

 generations, epigenesis or evolution, somatic origin 

 of germ-cells or germinal continuity from generation 

 to generation, these and many other fundamental 

 questions receive no certain replies from the study 

 of the development of the chick, and no discussion 

 in the pages of the book before us. What is a larva 

 and what an embryo? are natural questions for a 

 beginner to ask, but he will find no answer in the 

 work before us. He will not even read that, as 

 many embryologists think, the larva becomes the 

 embryo; still less as, wonderful to say, happened 

 recently in a well-known work, the embryo in its 

 turn could become a larva. From the account of 

 the rudimentary pronephros of the chick he will 

 be able to form no conception of what a functional 

 pronephros, such as that of the frog or newt, really 

 is. In short, it may be doubted whether from a 

 study of the development of the chick the beginner 

 can hope to obtain any real insight into the facts 

 and tendencies of modern embryology. 



The book is clearly written, and evidently much 

 labour has been expended upon its production, while 



