42 Journal of Comparative Neurology. 



tion of folds and villi in the alimentary tract and plexuses in the 

 brain ; or by expansion, and it seems to be the latter method 

 adopted in the brain of Auiia. In the formation of folds or 

 plexuses it is necessary for the blood vessels to intrude into the 

 brain cavity ; here the cavity has, as it were, come out to the 

 blood vessels. The same seems to be true of the metaplexus, 

 of Lcpidostais, and it is interesting to note that, whereas in Amia 

 the metaplexus is richly folded, in Lcpidostais it is entirely 

 smooth save for small folds at the sides. 



Careful examination of other Ganoids may reveal conditions 

 much like those existing in these two. Both Polyodon and Aci- 

 pciiser brains arc covered with a dense layer of connective tis- 

 sue which may involve such outgrowths of the diatela as here 

 described. Studnicka has recently reported that in Polypterus the 

 dorsal sack extends caudad as far as the cerebellum and the de- 

 scription and figures of Waldschmidt suggest strongly even an 

 exaggeration of the conditions in Anna. 



Paraphysis. — The presence of the paraphysis in Amia has 

 already been noted by Hill. In the adult it opens into the 

 cavity just cephalad of the velum (Fig. 4) and possesses many 

 tubular diverticula which occupy space in the velum (Fig. 3), in 

 the membranous roof of the prosencephal and in the caudal 

 part of the mesal fold. These are lined with a cubical or col- 

 umnar epithelium which, it is important to note, is of a differ- 

 ent appearance and easily distinguishable from the cells of the 

 dorsal sack and membranous roof. The paraphysis does not 

 seem to be a sack caused by or of the same nature as a plexus ; 

 on the other hand, neither is it an evagination of the same ap- 

 pearance and significance as the epiphysis and the view of His, 

 Kupffer, and Leydig ('96), that it really is an epiphysis, does 

 not seem correct ; the terms employed by them, vordere Epiph- 

 ysis and Epiphysis I, should not be confused with the anterior 

 epiphysis or epiphysis I used by others and in this article. The 

 paraphysis seems a structure in itself. The cells have indeed 

 the appearance of secreting cells, but of a nature different from 

 those of the surrounding epithelium. 



The paraphysis also exists in Ltpidosteiis, appearing much 



