SOME NEW BOOKS 



The Germ-Plasm : A Theory of Heredity. By August Weismann. Translated 

 by W. Newton Parker, Ph.D., and Harriet Ronnfeldt, B.Sc. Contemporary 

 Science Series. Pp. 477. With 24 illustrations. London: Walter Scott, 1893. 

 Price 6s. 



The new volume of Professor Weismann, of which the translation is 

 before us, departs from the historical method in which we have 

 received his work. This is a deliberate presentation of his theory, 

 incorporating, expanding, and explaining the ideas which have been 

 shaped in his various essays. At the same time, it contains a number 

 of novel hypotheses subsidiary to the theory, but necessary to'it. It 

 is not too little to say that the book is an excessively hard nut to 

 crack, and that many will declare the kernel bitter who have not 

 bitten through the epicarp. 



Speaking generally, this expanded account is a closer and more 

 detailed theory of the structure and mechanism of the germ-plasm, 

 bringing it closer into relation with, on the one hand, recent advances 

 in actual observation of the structures and changes in the nucleus 

 connected with cell-division, and on the other, with the observed 

 details of inheritance, variation, asexual reproduction and re- 

 generation of tissues. 



As before, the doctrine of the continuity of the germ-plasm is 

 firmly msisted on, and it may be said that this, of all parts of Professor 

 Weismann's theory, has been subjected to the least successful criti- 

 cism, and has received the most startling corroboration. This germ- 

 plasma Weismann identifies with the chromatin fibril in the nucleus 

 of egg-cells and sperm-cells. Before fertilisation, the nuclear fibril 

 breaks up into a series of loops which Weismann calls idants. In 

 ordinary sexual eggs the number of idants is twice halved, and by 

 what W^eismann calls these two reducing divisions the polar bodies 

 are extended. It will be remembered that, originally, the first polar 

 body was considered by Weismann to serve for the extrusion of that 

 part of the nuclear matter which, having served to guide the 

 maturation of the ovum, became useless when the ovum was mature. 

 In his completed doctrine, he finds in the two polar bodies of normal 

 sexual cells, and in the single polar body of parthenogenetic ova, a 

 mechanism for reducing the bulk of germ-plasm— part of the apparatus 

 for phylogenetic variation. The actual nuclear matter which controlled 

 the maturation of the ovum he supposes to have passed into the 

 protoplasm of the ovum, and, therefore, to be out of the reckoning 

 when the behaviour of the nucleus is being interpreted. 



When the nuclear loops or idants are closely examined they 

 exhibit a series of lumps or divisions as if they were built up of 

 separate pieces like draught counters strung together. These sepa- 



