The Pineal Region in Teleosts. 349 



points to the influence of Cranial development on the position of 

 this organ. 



The statement made by Goette ('75) that the pineal body in 

 Bombinator arises from a bridge which connects the brain and 

 ectoderm has repeatedly been reaffirmed and denied. Van Wijhe 

 ('83) and Hoffmann ('84) have presented evidence in support of 

 the connection; Mihalkovics ('77), Balfour ('85), and later inves- 

 tigators assert that the epidermal bridge has no existence. 

 Locy ('93) claims that the beginning of the epiphysis in the shark 

 can be seen in the medullary plate. No recent investigator has 

 found a continuity between the epiphysis and ectoderm after 

 the formation of the medullary tube, although a close relationship 

 has often been observed between the end of the pineal body and 

 the outer germ layer. This condition and the absence of any 

 intervening mesoderm led Hoffman to believe that the epiphyseal 

 anlage was laid out before mesodermal formation had commenced. 

 In Opsanus of 3.5 mm., when the epiphysis is just discernible, 

 a mesenchymal stratum stands between it and the ectoderm and 

 there is no evidence of continuity between these parts. 



Posterior Commissure 



It was shown in the descriptive part of this paper that the pos- 

 terior commissure, arising in the ectoglia layer of the brain-roof, is, 

 at first, located posteriorly to a pars intercalaris, that it spreads 

 forward over this region and finally becomes included within 

 the fold that intervenes between the mid-brain and diencephalon. 

 Moreover, it was found that the commissure in the older embryos, 

 in all stages, and in the adult fish, presents two distinct divi- 

 sions, anterior and posterior, separated by a connective tissue 

 septum. This mode of development has been observed in other 

 bony fishes, to which reference has been made above (p. 336), 

 and its division into strata has been described and represented 

 in figures of the teleostean brain. It appears, therefore, that a 

 type of posterior commissure appears among bony fishes, char- 

 acterized by the presence -of two strata of fibers separated by a 

 partition. The commissure lies neither altogether in the wall 



