Charles Sedgwick Minot 



93 



anterior surface of the velum, because these projections not only fix the 

 lateral boundaries of the paraphysal arch but also are the anlages of the 

 choroid plexus of the lateral ventricles. These anlages from this stage 

 on rapidly increase both in size and in complication of form. 



I wish now to add certain comparisons of the structures described 

 with those of other vertebrates, particularly with a view of determining 

 the homologies of the paraphysis, velum, and superior commissure. 

 Since Selenka's original brief announcement, 90.1, of the recognition 

 of the paraphysis as a distinct vertebrate organ, little has been added 

 to our morphological conception of it. It is completely ignored by the 

 standard German and English text-books, and Prenant in his Traite 



Rq.lS 



Fig. 13. Necturus maculatus of J 8 mm. 

 X 30 diams. 



Sagittal series, No. 23, section 90. 



d'Embryologie is the only author, known to me, who has attempted a 

 systematic analysis of the scattered observations. 



The paraphysis is a gland developed by a local evagination of the 

 epithelium of the paraphysal arch, and so far as known never is dif- 

 ferentiated as a sensory organ. 



As I have found no paraphysis in Acanthias embryos up to 86 mm., 

 we must have recourse to other types. I will mention first Necturus, 

 Fig. 13, and the chick. Fig. 14, as on these two forms I have made orig- 

 inal observations. In a Necturus of 12.0 mm. (Sagittal series 49, sec- 

 tion 60) the stage of the pineal region corresponds more or less to that 

 of acanthias shown in Fig. 3; the epiphysis is evaginated, and there is 



