THE PINEAL BODY 23 



Later, Beard ('87) 17 and Owsiannikow ('88) 295 following Ahl- 

 horn's lead, both spoke of two epiphyseal vesicles. Studnicka 

 ('99) 388 and Kupffer ('94) 224 showed that these two -vesicles were, 

 in fact, independent parts of the epiphyseal complex. Studnicka 

 called the anterior vesicle the parapineal organ and considered it 

 homologous to the parietal eye of reptiles. This he later con- 

 firmed in a subsequent work. Kupffer, however, saw in the 

 parapineal organ or parietal eye of reptiles the homologue of the 

 paraphysis in Petromyzon. Retzius ('95) 331B was the first to 

 employ the Golgi method in Petromyzon and Ammoccetes. 

 By this means he was able to demonstrate the nerve elements 

 of the stalk of these two epiphyseal organs. The finer structure 

 of the pineal and parapineal organs in Petromyzon marinus was 

 given by Leydig in 1853 231 and Studnicka in 1899, 3S8 while Johns- 

 ston in 1902 195 described these organs in Lampetra wilderi. 



2. The pineal region in selachians 



The pineal region in selachians is very similar to that of 

 Petromyzon with the exception that in the epiphyseal complex 

 the parapineal organ does not appear. The selachians are 

 remarkable for another fact, namely, that one member of this 

 class, Torpedo, develops no part whatsoever of the epiphyseal 

 complex; that is to say, both the pineal and parapineal organs 

 are wanting. 



In Notidanus, Burckhardt in 1890 42 distinguishes the follow- 

 ing parts: At the dorsal extremity of a thickened and invagi- 

 nated lamina neuroporica there appears a slightly developed 

 paraphysis. Immediately following this in the roof-plate there 

 is a marked invagination defining the velum transversum, which 

 appears in these forms as a simple infolding of the roof-plate 

 without any vascular development. The dorsal sac presents 

 itself as a more conspicuous element in the roof of this species 

 than in the cyclostomes. There is no anterior intercalated 

 portion and the epiphyseal complex shows only the presence of 

 the pineal organ. A short pars intercalaris posterior has been 

 described followed by the posterior commissure. This descrip- 

 tion given by Burckhardt in Notidanus holds true for most of 

 the forms of selachians with the exception of Torpedo. 



