FHKDKHICK TILNKV AND LUTHER F. WARREN 



d'Erchia ('96) 109 differentiated in Pristiurus the same elements 

 as in Notnlinins. but in Torpedo he found that the epiphyseal 

 complex was entirely wanting. He further observed that the 

 development of the velum transversum occurred much earlier 

 than the pineal organ. Minot ('Ol) 277 maintained that an actual 

 paraphysis does not develop in selachians. In comparing the 

 1 tinea! regions of cyclostomes with selachians, the most striking 



Po- 



Fig. 2 Schematization of pineal region in Selachians, according to Studnicka 

 1905. 



L.s-.. lamina tcrniinalis; Pf., paraphysis; V. velum transversum; D.s 1 .. dorsal 

 sac: !'>., pinoal organ; St., stalk of pineal or^an; Ch., commissura halicnul.-iris; 

 /.' . recessus pinealis; Cp., commissura posterior; Sclt., pars intercalaris posterior; 

 Prox., pniximal portion; '!'/>., Iractus pinealis. 



appear to be in the extreme development of the 

 parapineal and pineal organs in /'ilro/ni/zon and allied forms, 

 while the parapineal organ is ah-ciit in selachians. Further- 

 more. the absence of any distinct velum transversum in cyclo- 

 si. mies makes the presence of a definite paraphysis extremely 

 doubtful, while the velum transversum in selachians differen- 

 very clearly a fairly well formed paraphysis. The pineal 

 in Elasmdbranchs is much shorter than in Petromyzon. 



