402 CHARLES HILL, 



ledge here my great indebtedness to Dr. Locy, the Director, for constant 

 suggestions and for his interest and assistance during the whole period 

 of my work. The observations show the very early appearance of neural 

 segments and their identity with the neuromeres of Béraneck, Orr, 

 McClure and others. They show clearly in the earliest stages the 

 condition of the primary segments of fore- and mid-brains, and stages 

 in their modification up to the time the segments become obliterated 

 by the expansion of the brain wall of this region. 



The experience gained by the author in tracing the history of 

 the epiphysial vesicles in Teleosts (Hill, '91 and '94) afforded a 

 valuable and really essential preliminary training for the work in- 

 volved in this paper 1). 



3. Manipulation of Material. 



As the work contemplated the study of these segments first in 

 the living embryos, chick and Teleosts were selected. It should be 

 remembered such a study presents many difficulties. The study of a 

 single living embryo is necessarily limited in time. The material cannot 

 be laid aside and the observation repeated at a later date. Neither 

 as a rule is a comparative study of different ages possible. The 

 transparent nature of the embryos often leads to confusion because 

 segments of the two sides may appear indiscriminately mixed. This is 

 especially true of side views when studied under the compound micro- 

 scope. A good dissecting microscope gives in many ways better ser- 

 vice, as it enables the operator to manipulate his material to greater 

 advantage. This is especially true of preserved embryos when studied 

 as opaque objects where delicate shadows serve to detect seg- 

 ments. 



The following Teleosts ^) were studied : Salmo fontinaUs (Mitch.), 

 S. purpuratus (Pallas), S. fario (L.) and Coregonus alius (Ger.). 

 In order to repeat observations upon living material, cultures were 

 reared differing in age from 6 to 10 days. The temperature of the 

 lake water where these developed was 10 degrees colder than the 



1) As early as 1890, observations were begun by the author, on 

 neural segments of Teleosts, in the Universitj^ of Michigan, at the 

 suggestion of Prof. Reighard, but were discontinued in order to follow 

 the history of the epiphysial outgrowths in the same group of animals. 



2) I desire to express my thanks to the United States Board of 

 Fish Commissioners for liberal supplies of Teleost material. 



