446 



NATURE 



[July 3, 1913 



desires only a very general acquaintance with the 

 main lines of the historical development of the 

 science, without too much critical detail. Con- 

 sidering- the immensity of the subject, a great 

 amount of information has been packed into the 

 five hundred pages of which the work consists. 



The book is prefaced by a short biographical 

 note in which the main features of Dr. Brown's 

 character, and the chief incidents in what was 

 practically a lifelong connection with Liverpool, 

 are dealt with sympathetically. There is also an 

 excellent and characteristic portrait of the professor 

 by way of frontispiece. T. 



REPRODUCTION AND DEVELOPMENT. 



(1) Vertebrate Embryology : Comprising the Early 

 History of the Embryo and its Foetal Membranes. 

 By Dr. J. W. Jenkinson. Pp. 267. (Oxford : 

 Clarendon Press, 1913.) Price 12s. 6d. net. 



(2) Problems of Life and Reproduction. By Prof. 

 Marcus Hartog. Pp. xx + 362. (London: 

 John Murray, 191 3.) Price ~s. 6d. net. 



(1) T~\R- JENKINSON'S "Vertebrate Embryo- 

 1_^/ logy " will be welcomed by all students 

 of that subject in this country. Hitherto the 

 only book on embryology of convenient size and 

 suitable for elementary students has been Bryce's 

 volume in "Ouain's Anatomy," but this work is 

 devoted almost exclusively to human embryology, 

 and is avowedly intended for students of medicine 

 rather than for those taking zoology for an honours 

 degree in science. Dr. Jenkinson 's book will not 

 be without utility to the more advanced workers 

 in the subject, including original investigators and 

 teachers. To each chapter there is appended a 

 short bibliography which affords a valuable guide 

 to the literature. 



In the first chapter, which is introductory in 

 character, it is shown that the structural differ- 

 entiation which occurs in embryonic development 

 (and also in later life) takes place by movements 

 either of single cells or of cell aggregates, and 

 finally through the assumption by the cells of the 

 histological characters peculiar to each kind of 

 tissue. It is pointed out further that it is not a 

 process of cell division which produces the differ- 

 entiation, since differentiation already exists in the 

 ovum prior to segmentation, and is, indeed, the 

 real cause of the differentiations which subse- 

 sequently manifest themselves. The second 

 chapter is upon growth, and is illustrated by 

 figures of growth taken mainly from the work 

 of Minot, and showing the daily percentage incre- 

 ments in the weights of man and animals. 



Chapters iii. and iv. are upon the germ-cells, 

 and contain ndmirable accounts of the phenomena 

 NO. 227Q, VOL. Ql] 



of spermatogenesis, oogenesis, and fertilisation. 

 The author accepts the view that the germ-cells 

 are not all formed in or from the germinal epi- 

 thelium, but that the first to develop come from 

 the endoderm or splanchnopleure (mesoderm) of 

 the gut or yolk-sac, and reach their final resting- 

 place by migrating there. There is no mention, 

 however, of Miss Lane-Claypon's statements (at 

 present unconfirmed) regarding the origin of ova 

 from ovarian interstitial cells after the attainment 

 of sexual maturity. The author states that the 

 follicle cells are also probably derived from the 

 germinnl epithelium, but the recent work of Miss 

 Mcllroy is not quoted. In referring to the corpus 

 luteum, the author says that this organ secretes 

 a substance which appears to be necessary for 

 the proper attachment of the embryo by means of 

 the placenta. The theory has often been stated 

 in this form, but it now appears to the reviewer 

 that in a work like the present it might be better 

 to assert merely that the hypertrophy of the 

 follicle cells is functionally correlated with the con- 

 temporaneous uterine hypertrophy, which is a 

 necessary factor in the growth of the placenta 

 and the nourishment of the embryo, and cannot 

 occur in the absence of luteal tissue in the ovary. 

 The truth of the hypothesis stated in this general 

 form seems to be beyond question, whereas the 

 exact nature of the correlation is a problem which 

 stiil awaits complete solution. 



Space does not admit of more than a passing 

 mention of the succeeding chapters ; they deal 

 with segmentation, the germinal layers, the early 

 stages in the development of the embryo, the fcetal 

 membranes, and the placenta. The chapter on 

 the placenta is of especial interest, for Dr. Jenkin- 

 son writes with the authority of an original in- 

 vestigator. The physiological side of the subject 

 is not neglected, and there are new and interest- 

 ing details concerning the cestrous cycle. A word 

 must be added in praise of the numerous illustra- 

 tions, which, with verv few exceptions, were 

 drawn specially for this book. 



(2) Prof. Hartog's work consists of a collection 

 of essays contributed at various times during the 

 last twenty-one years to different journals, and 

 embodying his views on certain biological ques- 

 tions of importance. The majority of the articles 

 are republished with little alteration, but the 

 fourth chapter, in which the author's views on 

 the physics of cell-division are put forward, has 

 been almost entirely re-written. 



The first chapter is entitled " Some Problems 

 of Reproduction," and contains an account of 

 the author's theory as to the significance of the 

 polar bodies, which are regarded merely as the 

 products of brood-divisions of the ovarian egg. 



