562 LOCV. [Vol. XI. 



minute structure in the early stages, were those of Strahl and 

 Martin. Along this same line were the studies of Beraneck, 

 Francotte, Leydig, and others. By these investigators the 

 organ was traced backwards to a certain point in its history, 

 that is, to the time when it springs from the roof of the thala- 

 mencephalon as a tubular outgrowth, like the tip of a finger 

 of a glove. To this period also belongs the discovery of a 

 nerve of transitory existence. The investigations were con- 

 fined almost entirely to two groups of animals, Amphibia and 

 Reptilia. In the embryos of these animals many points of 

 minute structure were worked out, such as the distribution 

 of the nerve within the eye-like capsule, the division of the 

 retinal part into distinct layers, the fact that the pineal eye is 

 higher developed in the embryonic periods than later, etc. 



The next step was the discovery that there is more than one 

 epiphysial outgrowth. Selenka, Leydig, Eycleshymer, Hill, 

 successively called attention to the existence of two distinct 

 outgrowths, or vesicles, from the roof of the thalamencephalon 

 in Anguis, Amblystoma, and Teleosts. 



Hill's studies on these two vesicles are the most complete. 

 He has shown the existence in Teleosts and Amia of two 

 vesicles, anterior and posterior, and has traced them through 

 the stages of development. The posterior develops into the 

 epiphysis and the anterior degenerates. The distal portion of 

 the former is histologically very complex, and receives a nerve 

 from the posterior commissure. Hill made out the distribution 

 of nerve-fibres in this part of the epiphysis. He traced quite 

 clearly the history of the vesicles. 



Two vesicles, an upper and a lower, have long been known 

 to exist in Petromyzon, in both embryos and adults. It is 

 much to be regretted that we do not know their embryonic 

 history, for much depends on this. The most recent paper on 

 the epiphysial organs in Petromyzon — that of Studnicka — 

 does not Clear up the question of the origin of the two vesicles. 

 Histological material was lacking in just the stage required. 

 The two Outgrowths in embryos outside the Cyclostomes have 

 been designated epiphysis, for the hinder, and pineal eye for 

 the anterior. Studnicka designates them pineal and parapineal, 



