The Pineal Region in Teleosts. 347 



post-velar arch) as the median dorsal part of his parencephalic 

 segment which in turn, he derives from the second neuromere. 

 The same author finds the intercalated part to be the roof of his 

 synencephalic segment, derived from the third neuromere. Re- 

 garding the relation of the epiphysis to these segments, Kupffer 

 ('06) says: ^'Es tritt namlich die Commissura posterior, die man 

 als dorsale Grenzmarke zwischen dem Vorder und Mittelhirne 

 festzuhalten hat, nicht zwischen den Segmenten p and se auf — 

 hier entsteht die Epiphyse" (p. 175). The segments J9 and se 

 are the parencephalic and synencephalic segments. The para- 

 physis is the product of the telencephalic segment derived from 

 the first neuromere, and the velum marks the dorsal boundary 

 between the telencephalic and parencephalic segments. According 

 to Johnston ('05) the second neuromere gives rise to the optic 

 vesicles; from its narrow dorsal part is formed the velum. The 

 epiphysis, according to this author, belongs to the third neuro- 

 mere. 



Epiphysis 



The two epiphyseal outgrowths of Opsanus differ in their early 

 form and relations from those of Salmo, Coregonus and the other 

 teleosts which Hill ('91, '94) studied. In the first place they are 

 not true evaginations but solid outgrowths of the brain-roof. 

 As in the case of the solid epiphysis of Clupea, a cavity traversed 

 by fibers is later formed in the main organ. Holt ('91) regarded 

 the fibers as a coagulum and found no eye-like structure in the 

 epiphysis, but Studnicka ('05), who looks upon the two walls 

 of the pineal vesicle of Peftomyzon as retina and pellucida, hints 

 at a comparison of these syncytial nets with the remains of 

 a corpus vitreum of the parietal organ. The network in Op- 

 sanus is derived, as already shown, from the lightly staining pro- 

 toplasm occupying the axis of the epiphysis, and it therefore 

 cannot be considered a coagulum of some possible secretion of 

 the walls of the organ. A secretion discharged into the cavity of 

 the epiphysis of Opsanus would have no outlet. While the organ 

 is moderately vascular it does not conform in structure with any 

 of the ductless glands. On the other hand there is little evidence 



