136 

 gre=it masses of cytoplasm /rhioh lie lat?r=il to the nucleus. 

 The nucleus is eccentric in position, leaving but a thin pel- 

 licle of cytoplasm on one of its si'ies. The chromatin is group- 

 ed into a fef stranis having conspicuously thickened nodes at 

 intervals. 



i. Geieral Oonsi ierat ions on the Pallium.-- The pallium 

 Of the selachian is really a primitive representative of the 

 stem giving origin to the pallia of amphibians, reptiles, birds, 

 and mammals. The continuity of its t'.vo halves, contrasted .vith 

 the two-lobed condition of the higher type, has caused many 

 /writers to rank the selachian pallium as a divergent branch. 

 The correctness of tne vie'? set forth in this paper v»ill appear 

 «hen the significance of the relations /fhich exist between 

 certain neurones of Mustelus have been considered. 



It has been shown that the ventral border of a lateral 

 ventricle is the seat of one olfactory termination, the epi- 

 striatum. The epistriatua tends to become extended around the 

 siie of the ventricle towarl the pallium. Axones from the 

 marginal neurones of this olfactory centre enter the pallium, 

 thus serving to link that region indirectly with the olfactory 

 organ. Besides this source of impressions, the olfactory centre 

 of the nucleus neuroporicus radiates an influence to the pal- 

 lium, of which it is really a part. The pallium of Mustelus, 

 therefore, is seen to have a general association with the olfac- 

 tory mechanism. 



