220 FREDERICK TILNEY AND LUTHER F. WARREN 



Histological evidence in ganoids. The pineal organ alone 

 develops in ganoids, although in a single Jorm, namely, Amia, 

 an abortive parapineal organ makes its appearance. The end- 

 vesicle of the pineal organ in ganoids generally shows some 

 tendency toward the development of a retinal or pellucidal 

 layer, although neither of these is well marked-. Studnicka, 391 

 as the result of his studies upon ganoids, does not believe that 

 there is any evidence of glandular activity in the end-vesicle 

 or proximal portion which is at all comparable to that of the 

 corresponding parts in selachians. On the other hand, he does 

 not deny that there may possibly be secretory function in the 

 pineal organ of ganoids. 



Histological evidence in teleosts. The epiphyseal complex in 

 teleosts differs from that in selachians and ganoids in being a 

 much larger structure. The end-vesicle, furthermore, mani- 

 fests, in nearly every species, a pronounced tendency toward the 

 convolution of its walls. Not only is this process apparent 

 upon the surface, but section of the vesicle shows it to consist 

 of many folds and diverticula, all of which give to it the appear- 

 ance of a tubular gland in communication with the third ven- 

 tricle by means of a long hollow stalk. Galeotti 140 in Leuciscus 

 found evidence of secretory activity in the presence of fuch- 

 sinophile granules similar to those described by him in selach- 

 ians. The product of this secretion, he thinks, is delivered to 

 "the lumen of the end-vesicle and thus to the ventricle of the 

 diencephalon. Studnicka 391 observed cells having a similar 

 appearance, and although he did not commit himself definitely 

 as to their nature, he nevertheless expressed the belief that the 

 organ is not entirely a gland. Some nerve fibers of the stalk 

 seem to represent a rudimentary pineal nerve. 



Histological evidence in amphibia. The first recognition and 

 description given by Stieda 379 in which he called the end-vesicle 

 a frontal subcutaneous gland was evidently a misinterpretation 

 of the conditions in amphibia. The end-vesicle in these animals 

 is fairly well developed, presenting a retina and lens which, 

 although clearly recognizable as such, have attained scarcely 

 more than an abortive state in their development. A long 



