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SOME NEW BOOKS. 



Hertwig versus Weismann. 



The Biological Problem of To-day. By Dr. Oscar Hertwig ; translated by 

 P. Chalmers Mitchell. Crown 8vo. Pp. xix., 148. London: Heinemann, 1896. 

 Price 3s. 6d. 



This work will be greeted with satisfaction by all who are interested 

 in the problem of heredity. In translating Professor Hertwig's book, 

 Mr. Chalmers Mitchell has rendered a service to the ordinary reader 

 who may not have the power or inclination to read it in the original. 

 As most people are aware, Hertwig has long been the foremost oppo- 

 nent of Weismannism ; indeed, the present work is largely devoted 

 to refuting the doctrine of the Freiburg zoologist. The translator 

 has prefixed a clear and concise statement of the case as it now stands 

 between the two chief schools of thought. He has, however, carefully 

 refrained from giving any opinion of his own. This is, perhaps, a 

 matter for regret. Mr. Mitchell is known as a student and expounder 

 of Weismann's views, and an opinion from him as to the merits of an 

 opponent doctrine would not have been out of place. There is, at 

 the end of the book, a glossary of technical terms which will commend 

 itself to the non-scientific reader. 



The book itself is, like all the works of its distinguished author, 

 a model of clearness and simplicity ; and the doctrine of epigenesis 

 as opposed to that of evolution is forcibly stated. The opening 

 pages introduce the subject of heredity, and state the position occupied 

 by Weismann. Further on, the fundamental point is dealt with as 

 to whether, in a dividing cell, there is a quantitative or qualitative 

 division of the nucleus ; with a decision in favour of the former. 

 That is, each chromosome splits into two exactly equal and like halves, 

 and in no case is there any dissimilarity of structure or properties 

 between them. To prove his case, the author deduces arguments 

 from several groups of facts, especially those dealing with the 

 reproduction of unicellular organisms, and the phenomena of re- 

 generation and heteromorphosis. He next attacks Weismann's 

 doctrine of " Determinants," and points out the logical fallacy in 

 assuming that all the characters present in the adult organisms should 

 necessarily be predetermined in the germ plasm. Such a view results 

 from a failure to distinguish between the causes contained in the egg 

 at the beginning of development, and the causes entering it during the 

 course of development from the taking up of outside material. Thus 

 Hertwig combats the one view of Weismann's that his supporters 

 have found most hard to accept, viz., the almost total indifference of 

 the germ plasm to external surroundings or stimuli. 



The latter half of the book gives a plain statement of the author's 

 own views as regards the causes which determine the development of 

 organisms. Quoting from botanists and zoologists, he seeks to show 

 that development is due to external influences acting on a highly 

 complex germ plasm, capable of almost infinite alterations in form 



