236 FISH. [Vol. X. 



nection with the difficulty of removing so small an object 

 without injury, renders microscopical methods a necessity. 

 The study of the general topography, the relations of the 

 cavities and other parts is greatly facilitated by the use of a 

 series of enlarged camera lucida drawings or the construction 

 of models in wax or otherwise. 



Barring its size, the general simplicity of the amphibian 

 brain would render it a most admirable object for the study of 

 morphological relations ; its general absence of flexure, its 

 successive segmental arrangement and the degree of exposure 

 and differentiation of these segments, give it a great advantage 

 over most other generalized forms. The brain of Desmogna- 

 thus fusca is a slender elongated organ, its widest point 

 being at the latero-caudal ends of its hemicerebrums or at 

 about the middle of its length ; the general dorsal surface is 

 nearly on the same plane, most of the segments being exposed. 

 The lateral regions, especially of the prosencephal, slope quite 

 abruptly toward the ventrimeson (ventral median line), so that 

 if a transection be made in this region a triangular outline will 

 be the result, the base being dorsal and the apex ventral. 

 The ventral aspect is much more broken and irregular. 



There is no evidence of a cranial flexure ; the pons flexure 

 persists and there is likewise some evidence of a neck or 

 cervical flexure. Assuming that the diencephal and mesence- 

 phal are the fixed portions of the brain axis, and that there is 

 a greater rate of growth of the parts cephalad and caudad of 

 them, we can perhaps arrive at some explanation of the 

 arrangement of the parts. The metencephal in its more rapid 

 growth longitudinally would tend to grow under and around 

 the caudal half of the mesencephal and become overlapped by 

 it ; while in the case of the prosencephal, during its dorso- 

 caudal growth the hemicerebrums would tend to divaricate 

 and overlap the diencephal to some extent laterally and give 

 the latter a wedge-shaped appearance. The whole brain then, 

 as seen from the side, might compare slightly in outline with 

 a \ . So that in this form there is a departure from 



the straight and unflexed condition as exemplified by the most 

 of the aquatic urodeles. On the dorsal aspect, the large supra- 



