96 FEEDERICK TILNEY AND LUTHER F. WARREN 



5. Mustelus Icevis. Cattle ('82). 60 In this form the pineal 

 organ is extremely simple, consisting of an end-vesicle, a stalk, 

 and a proximal portion. The end- vesicle is flat and shows no 

 tendency toward reduplication. 



6. Centrophorus granulosus. Cattie ('82). 60 The end- vesicle 

 in this form has a hammer-shaped appearance. The stalk is 

 strand-like and the proximal portion conical. The pineal organ 

 is hollow throughout its entire course. A marked parietal 

 depression lodges the structure and this is surrounded by con- 

 nective tissue. 



7. Lamna cornubica. Carrington ('90). 58 This form pre- 

 sents an end-vesicle which is conical and a stalk which is cylin- 

 drical. Both contain an irregular lumen. The ventral wall of 

 the end- vesicle is thicker than the dorsal wall. The cells in this 

 vesicle are for the most part ependymal, although there are 

 many others scattered among the cells of this character. The 

 pineal organ is lodged in a depression surrounded by connective 

 tissue and there is a corresponding slight depression in the epi- 

 thelium above the organ. 



8. Spinax niger. Studnicka ('93). 384 In embryos, larval and 

 adult forms, this species presents all three portions of the pineal 

 organ. It is slender and directed at right angles to the roof- 

 plate in the embryo, is slightly bent in larval forms, and is 

 flexed at right angles in adults. The end- vesicle is pressed into 

 a cartilaginous skull, although there is no actual parietal fora- 

 men. The parietal portion consists of ependymal cells and 

 neuroglia cells. A parietal spot is present in the form of an 

 oval white area. There is, however, no parietal cornea. 



9. Notidanus griseus. Studnicka ('93). 384 The entire pineal 

 organ in this form is sharply flexed forward above the forebrain. 

 The proximal part is not particularly developed, but in other 

 respects has the same general form as other species. 



10. Pristiurus melanostomus. d'Erchia ('96) 109 and Minot 

 ('01). 277 Here the pineal organ extends directly forward in the 

 horizontal plane above the forebrain in the midsagittal plane. 

 The end-vesicle is much attenuated and the stalk is merely a 

 strand-like connection between the former and the roof-plate 



