98 FREDERICK TILNEY AND LUTHER F. WARREN 



5. Torpedo ocellala. d'Erchia ('96). 109 No evidence of de- 

 velopmental differentiation into a pineal organ was found in 

 the early stages of this form. A well-developed paraphysis, 

 however, is present. 



HOLOCEPHALI 



1. Callorhynchus. Parker and Haswell ('97). 302 



2. Chimaera monstrosa. . Studnicka ('96). 386 In both of these 

 forms there is a well-defined epiphysis and a large dorsal 

 sac. The pineal organ has a form similar to other selachians; 

 that is to say, a fairly well-marked proximal portion, a long, 

 slender stalk extending forward and expanding slightly to form 

 an end-vesicle at its extremity. 



In all, seventeen species of selachians have been examined; 

 that is, ten Elasmobranchs, five Rays, and two Holocephali. 

 In two species a complete absence of the pineal organ is reported, 

 namely, Torpedo ocellata and Torpedo marmorata. All of the 

 other species present a pineal organ more or less well developed. 

 In one form, that is, Galeus canis, histological evidence has been 

 presented showing that there is some reason to believe that a 

 secretory function obtains in the pineal organ of this form. 

 Wherever mention is made of the paraphysis it seems to be an 

 organ of considerable size. 



3. Comparative anatomy and histology of the epiphyseal complex 



in ganoids 



In all the species of Ganoids there develops a fairly well- 

 marked pineal organ. In one form only, namely, Amia, is there 

 any indication of the presence of a parapineal organ. Stannius, 373 

 giving the first description of the structure of the parapineal 

 organ in Acipenser sturio in 1854, states that the structure is a 

 wide evagination extending from the roof of the interbrain and 

 connected with the commissura habenularis. It reaches for- 

 ward to a fossa in the roof of the skull. Cattie 60 in 1882, also in 

 Acipenser sturio, and Goronowitsch 153 in 1888, on Acipenser 

 ruthenus, gave similar descriptions of the pineal organ. Gar- 

 man 143 in 1896 and Johnston 194 in 1901 by means of the Golgi 



