10 

 to be recognized as valuatle means for hardening; nervous tis- 

 sues. Fortunate that man who was permitted to contrilute to 

 the inauguration of a new era in the comparative study of the 

 nervous system, the era of microscopicel research. Two inves- 

 tii^ators extended such a possibility to the field of the sela- 

 chian brain at practically the same time, Viault publisliing 

 his results in 1376, and Bohon in 1877. 



The research of Via.ult ('7*^) is quite broad in its scope. 

 It includes a review of the anatomical features of the sela- 

 chian nervous system; a description of the structural elements 

 common to all nerve-centres; topographic histology, or the 

 structure of the several parts of the brain and cord; and, 

 finally, a consideration of the homologies of the brain-segments. 

 The figures which accompany the paper are perfectly clear in 

 their execution, but they represent such a low degree of magni- 

 fication that they are really little more than diagrams. While 

 the observations recorded by this author are of the most general 

 character, he should receive great credit for interpreting the 

 brain-segments properly at a time when there was much confusion 

 in this respect. 



In the prosecution of his research, Rohon ('77) had all 

 the stimulating advantages of the laboratory of Glaus, and his 

 work has a high order of merit. There is a section devoted to 

 the comparative anatoniy of the cranial nerves and the several 

 regions of the brain, in both the rays and the sharks. Certain 

 figures illustrating this portion of the work are familiar to 



