LITERARY NOTICES. 



The Derelopmeiit of the Brain and Sense-Organs in Elasmobranchs." 



This well-prepared paper is somewhat misrepresented by its title, 

 for it is in reality, in so far as concerns the original portions, a study of 

 metamerism of the brain and the origin of certain sense organs based 

 on embryos of Squalus acanthias. The questions to which this paper 

 addresses itself are sufficiently ambitious, being such as the following : 

 (i) What was the primitive condition of the nervous system of verte- 

 brates ? (2) What were the number and nature of the primitive neural 

 segments entering into the brain? (3) What has been, in general, the 

 line of modification along which they have been converted into the brain? 

 (4) What were the early steps in the differentiation of the sense-organs? 

 This is certainly a program calculated to awaken high expectations and 

 it is no detraction from the genuine excellence of what is offered to 

 admit that the materials and their employment are undoubtedly inade- 

 quate to its fulfilment. The paper does, however, give very useful 

 summaries of the historical development of those phases of the sub- 

 jects which are taken up. 



I'he earlier part of the paper is occupied with the problem of 

 metamerism. The author apparently agrees with McClure in mini- 

 mizing the segmental value of the cranial nerves because of the uncer- 

 tainty due to the degenerations of certain branches and even entire 

 nerves. This may appear inconsequent when he, at the same time, 

 explains the segmentation of the tube as due to the cranial nerves. 

 This criticism is not necessarily valid, however, for it may be true that 

 the segmentation of the brain was originally due to the concentration 

 of nervous matter adjacent to the point of development of the segmen- 

 tal nerves and yet this segmentation might persist in an early stage of 

 animals in which the subsequent development processes had been di- 

 verted. In other connections, however, the author fails to avail him- 

 self of this possibility. Professor Locy does not admit that the seg- 

 mental divisions of the middle germ layer are primitive. He accepts 



* LocY, Wm. a. Contribution to the structure and development of the 

 vertebrate head. Jotirn. Morphology, XI, 3, 1895. 



