352 Robert J. Terry. 



ependymal epithelium which appears to consist of secreting cells, 

 and Herrick ('91) describes the pouch of the diatela as possesed 

 of a wall composed of a single row of cells with long cilia or flagella. 

 It appears, therefore, that in these ganoids the epithelium of the 

 arch is especially modified and lines a great evagination of the 

 diencephalic roof. Regarding the elasmobranchs, Minot ('01) 



says '' the post-velar arch remains small, hence the 



velum seems to arise later very close to the mouth of the epiphysis." 

 The connection of the smaller epiphyseal bud with the post- 

 velar arch by forward shifting brings up the question of its possible 

 relationship with those large outgrowths of this region which have 

 been observed by Schauinsland (SeeKupffer, '06) inCallorhynchus, 



V 



by Gierse ('04) in Cyclothone, and by Handrick (See Studnicka, 

 ,'05) in Argyropelecus. Commenting on the latter, Studnicka, 

 ('05) says: ''Der Fall ist sehr wichtig, da er zeigt, dass der de 

 norma breitere Dorsalsack unter Umstanden sich in ein enges 

 schlauchformiges Gebilde verwandeln kann. Dieselbe Er- 

 scheinung kann man bekanntlich auch beiderParaphysebeobach- 

 ten; auch diese tritt einmal als ein enger Schlauch, ein anderes 

 Mai wieder in der Gestalt eines breiten Sackes (Paraphyseal- 

 bogen — Sedgwick Minot) auf." 



Velurn Transversum 



The velum transversum of the teleosts, according to the current 

 descriptions, consists of a simple transverse fold of the fore-brain 

 roof, having smooth surfaces and a free ventral margin. Rabl- 

 Ruckhard ('82) regards the velum as the starting point, phylo- 

 genetically, of the choroid plexus, although he found no differen- 

 tiation in this direction in the bony fishes. In them this organ 

 seems to be less advanced in its development than it is among 

 the selachians, where it has been shown that projections are formed 

 on either side which are regarded by Minot ('01) as the anlages 

 of the choroid plexuses of the lateral ventricles. In Acanthias a 

 superficial coat appears upon the ependyma of the anterior 

 surface of the velum, the nature of which is uncertain, but as 



