:?EPTEMBER 2^, IQI/] 



NATURE 



63 



of each other. It is pointed out that .this separa- 

 tion gives rise to partial larvae only, when, owing 

 to the direction of the cleavage planes, different 

 cytoplasmic substances are thereby separated from 

 each other. We may note in passing that an 

 error has been committed by Dr. Jenkinson in 

 dealing with eggs showing the spiral type of 

 cleavage. He states that the nephridia of the 

 earthworm are derived from descendants of 2d (an 

 -ectodermal cell), but those of the leech from cells 

 which are daughters of 4^ (the mother-cell of the 

 ccelomic mesoderm). The fact is that it was in the 

 development of the leech that Whitman first 

 demonstrated the ectodermal origin of the ne- 

 phridia, and this was proved to be true for a near 

 relative of the earthworm (Criodrilus) by Staff. 

 In both cases 2d or its homologue is the mother 

 of the nephridia. 



The third lecture has as its title "Differentia- 

 tion," but it really overlaps to a large extent the 

 second, and is occupied to a considerable degree 

 with the potentialities of isolated blastomeres. The 

 subject of the development of polyspermia eggs is 

 then taken up, and the conclusion is reached that 

 normal development is only possible if each blasto- 

 mere into which the ^^^ divides receives a 

 full set of the reduced number of chromosomes. 

 Dr. Jenkinson then considers the results of the 

 cross-fertilisation of eggs of sea-urchins with the 

 sperm of forms belonging to distinct genera, orders, 

 and even classes, and arrives at the conclusion 

 that the broad outlines of structure are inherited 

 through the female, and that the male only hands 

 on specific characters. This idea rests on the fact 

 that the foreign sperm is unable to transmute the 

 maternal cytoplasm into a being belonging to a 

 totally different class. But although the cyto- 

 plasm has had its properties determined by the 

 maternal nucleus during the ripening of the ^^^, 

 yet the hybrid organism, which in most features 

 conforms to the maternal type,- never survives the 

 early larval stage, at which period the "main 

 features " of its adult organisation are not even 

 indicated. There are also instances, such as the 

 cross between Echinocardium and Echinus, where 

 paternal influence can be detected at a very early 

 period of development. 



Dr. Jenkinson allows only a few pages for the 

 most interesting department of experimental 

 -embryology, viz. the interaction of parts on one 

 another — or formative stimuli. We can only 

 heartily agr^e with his conclusion that this is a 

 factor in development of the utmost importance, 

 on which more work is urgently demanded. 



{2) Prof. Brachet's little primer is one of the 

 most fascinating volumes which we have ever 

 read. The author was professor at the Univer- 

 sity of Brussels when the war broke out, but 

 ■whether or not he is a Frenchman by race, he 

 writes with all the clarity of thought and ex- 

 pression characteristic of the best French scientific 

 men. He succeeds within moderate compass in 

 giving a bird's-eye view of the principal results 

 which have been obtained by the experimental 

 method in embryology, without launching into un- 

 NO. 2500, VOL. 100] 



necessary detail. His object is to answer, so .far 

 as our knowledge permits, two questions, viz. 

 (i) How does the spermatozoon start the develop- 

 ment of the ^g^"^ and (2) How is the development 

 guided when it has begun? 



Vyith most of his conclusions we should be 

 inclined to agree, and if we must demur to one or 

 two of his deductions it is only fair to add that 

 again and again he reminds us how imperfect is 

 our knowledge in this department of zoology, how 

 few are the types of eggs that have been experi- 

 mented with, and therefore how provisional must 

 be our theories. For this reason he will not even 

 dignify them with the name of theories, preferring 

 the more modest appellation "hypotheses." 



It is natural that each writer on experimental 

 embryology should give a large place to the re- 

 sults obtained from the type of e:^^ with which 

 he is familiar, and just as Driesch's thought has 

 always centred in the sea-urchin's e.^^^ so Brachet 

 in this volume dwells principally on the frog's 

 egg, with the development of which he has chiefly 

 occupied himself. He arrives at the conclusion 

 that the influence of the spermatozoon can be 

 analysed into four separate actions, (i) It brings 

 into the t^^ a centrosome which initiates the 

 division of the ^^^ nucleus. (2) By its unioa 

 with the z^^ nucleus it restores the proper nucleo- 

 plasmic relation, and so enables the incipient 

 tendency to divide to be carried through to a 

 successful conclusion. (3) It causes a rearrange- 

 ment of the organ-forming materials, and so 

 determines the axes of symmetry of the embryo. 

 (4) It transmits the special hereditary qualities 

 of the father. Brachet holds the view, which, as 

 we have seen. Dr. Jenkinson is also inclined to 

 favour, that the main features of the embryo are 

 determined by the cytoplasm of the ^^^, and are 

 therefore purely maternal, all that is transmitted 

 from the father being the smaller details which 

 characterise his individuality. We have already 

 indicated the reasons which compel us to dissent 

 from this view. 



Limits of space unfortunately forbid us to touch 

 on many of the interesting points contained in 

 the volume, such as the resolution of Driesch's 

 entelechy into the results of surface tension, or 

 the demonstration of the means by which poly- 

 spermy is prevented in normal development — 

 which differ widely from Lx>eb's view on the same 

 subject. We can only say, in conclusion, that a 

 rich treat awaits the reader of this volume. 



E. W. M. 



OVR BOOKSHELF. 



La Force et le Droif. Lc Prctendu Droit Bio- 

 lofriquc. Par Prof. R. Anthony. Pp. 194. 

 (Paris: Felix Alcan, 1917.) Price 2.50 francs. 

 Prof. R. Anthony, well known for his fine 

 studies of arboricolous animals, and for his 

 insistence on the evolutionary importance of an 

 arboreal apprenticeship in the case of man's 

 ancestors, has made an elaborate criticism of the 

 view that there is biological justification for 



