The Pineal Region in Teleosts. 339 



anterior part of the commissure rests upon the intercalated divi- 

 sion of the diencephalic roof, reaching forward to the base of the 

 epiphysis. The posterior division forms a superficial fiber layer 

 of the mid-brain in this region. 



Velum Transversum. The middle lobe of the velum is relatively 

 larger than in the preceding stage. In its growth backward it 

 has invaded the region of the post- velar arch and has come there- 

 fore to lie below the epiphyseal stalk and the intercalated part of 

 the diencephalon. The lobules comprising it are numerous and 

 each includes a blood sinus whose walls are closely related with the 

 epithelial covering of the velum. 



Post-velar Arch. The reduction of this region, already referred 

 to, goes hand in hand with the backward growth of the velum. 

 The latter appears to have taken up and included the epithelium 

 of the arch. That this process takes place was however not proved, 

 for the epithelium of the arch presents no characters by which 

 it can be distinguished from that of the pedicle and base of the 

 velun: . 



Paraphysis. The thick epithelial coat of the velum passes 

 over into the roof of the telencephalon for a short distance, giving 

 place to the flat epithelium of the tela. Where this change occurs 

 the roof is elevated into a slight but conspicuous transverse fold 

 lying just beneath the end of the epiphysis. This rudimentary 

 paraphysis presents a simple structure, consisting, as in the pre- 

 ceding stages, of a rather high epithelium, resting upon a thin 

 stratum of connective tissue which contains but few vessels. 



Opsanus Larvae of 19 mm. in Length 



Epiphysis. The forward inclination of the epiphysis is more 

 marked than in the preceding stage. The elongated stalk, bent 

 over the superior commissure, is continued into the now much 

 enlarged end-vesicle. In the latter a cavity is to be seen for the 

 first time. This space, occupying the region which in earlier 

 stages was characterized by the presence of clear, non-nucleated 

 protoplasm, is traversed by fine fibrillae continuous with the 

 surrounding walls (fig. 16). The conclusion that these fibrils 



