The Pineal Region in Teleosts. 353 



Minot says ('01, p. 91), '' . . . suggests . . . the for- 

 mation of secretory spherules." Gentes ('08) regards the -velum 

 of torpedo as a true choroid plexus. The enormous development 

 of the velum of Opsanus is a striking peculiarit}^ of the brain of 

 this bony fish. The more important structural characters which 

 have been described on p. 342, seen in all the adult and larval 

 specimens, are those belonging to the true choroid plexus and 

 establish the velum of the toad-fish as such an organ. 



Among the teleosts possessing a rudimentary velum, Belone 

 acus has been cited by Studnicka ('05) . In the brain of the Ameiur- 

 us embryo, shown in fig. 20, the velum is rudimentary and there 

 is a further resemblance to Belone in the peculiar form of the epi- 

 physis. This consists of a large flattened end-vesicle supported 

 upon a rather slender and tortuous stalk. As to the significance 

 of the primitive velum the view recently expressed by Johnston 

 ('09) is interesting, namely, that the velar invagination begins 

 early ''on account of the withdrawal of material from the alar 

 plate to form the optic vesicle." With such a relationship between 

 these structures, some variation in the development of the 

 optic vesicle might be expected in those animals where the velum 

 is rudimentary or absent. 



Paraphysis 



The occurrence of a paraphysis in a number of teleosts, as 

 discovered by Burckhardt and Studnicka, lends support to the 

 interpretation that has been given to the fold of the fore-brain 

 roof in Opsanus. The higher epithelium of the fold differentiates 

 this rudimentary organ from the tela anterior to it, and its posi- 

 tion, immediately in front of the velum, corresponds with the loca- 

 tion of the paraphysis in all forms in which it has been observed. 

 This relation of paraphysis and velum or choroid plexus is respon- 

 sible for the identity of the former organ remaining hidden for so 

 long a time. In Opsanus the paraphyseal fold is clearly no part 

 of the velum for it appears after the latter has been formed, 

 differs from it in structure and has only a brief existence. 



The part of the embryonic fore-brain roof which is to give rise 



JOURNAL OF MORPHOLOGY, VOL. 21, NO. 3. 



