298 Susanna Phelps Gage 



larval diemyctylus. The development of the cerebral com- 

 missures (p. 281) will undoubtedly throw further light on the 

 question of the rhinencephal as a separate segment. 



SUMMARY. 



1. A true metapore exists in adult diemyctylus and indi- 

 cations of it appear in larvse. In lamprey and amia at a cor- 

 responding part ot the metaplexus a sac communicating with 

 the metaccele protrudes over the myel. 



2. The callosum and the callosal eminence are only begin- 

 ning to develop in early larvse of diemyctylus, and the posi- 

 tion of the cerebral commissures differs, in earlj' stages, more 

 from the anurous type than does the adult, the aula being 

 much larger proportionately. The type in urodeles and fishes 

 may be one of an arrested embryonic development. In the 

 diemyctylus there is evidence, in the adult, of a caudal growth 

 of the terma which if continued would bring the commissures 

 in the same relation to the terma as in the frog and higher 

 forms. 



3. The crista in diemyctylus and amia is shown to be a defi- 

 nite structure beyond which the cerebrum develops cephalad 

 and from over which the auliplexus is reflected, and thus is a 

 landmark in discussing the relations of the aula and cerebral 

 commissures. 



4. The paraphysis of diemyctylus is traced through differ- 

 ent stages of development and homologies discussed in amia 

 and lamprey, and a possible use in the nourishment of the 

 brain is suggested. 



5. Sulcus is proposed as a general term for the furrows on 

 the endymal surface, which have a morphological significance, 

 and lophius for the ridges between sulci. 



6. In the discussion of the geminums it is shown that 

 homologies are not dependent upon the membranous or solid 

 condition of the roof nor the angle at which the parts unite. 



7. The morphological relations of the pallium are considered 

 in amia and its homolog in amphibia and lamprey suggested. 



8. The cerebrum of amia and other fishes is not to be 

 considered from its recurved position as different from other 



