572 LOCK [Vol. XL 



kowstrom might be brought about, and still not be inharmoni- 

 ous with the other observations. The two vesicles might, in 

 earlier stages than he represents, have been formed independ- 

 ently, side by side, and thrown into communication by an 

 upward growth of the brain roof involving them both. Or, 

 indeed, there may be variations in the details of the forma- 

 tions of these two vesicles. 



However this may be, the results of the different observers 

 all go to show conclusively that there are two (not counting 

 the paraphysis) distinct outgrowths from the roof of the thala- 

 mencephalon of Petromyzon, Teleosts, and Lacertilia. The 

 fate of the anterior vesicle varies in the different groups, while 

 the posterior one persists in all as the epiphysis. The anterior 

 one may be formed as a rudimentary organ of transitory exist- 

 ence, as in Teleosts ; or it may be developed into the pineal 

 eye, in front of the epiphysis, as in Lacertilia. 



The sources of nerve-supply to the two vesicles have been 

 made known in Cyclostomes, Teleosts, and Lacertilia, and 

 these facts are important in establishing homologies. It has 

 been shown (Studnicka, Gaskell, Klinckowstrom) that the 

 upjDcr capsule of Petromyzon receives its nerves from the 

 posterior commissure, and that the lower vesicle is innervated 

 from the left ganglion hebenula. Hill, in embryos of Teleosts, 

 has traced a nerve from the posterior commissure into the 

 epiphysis and has studied its distribution in detail in that 

 structure. The anterior vesicle of Teleosts disappears before 

 it has formed any nerve connection with the brain. 



Klinckowstrom ('93) has observed very interesting conditions 

 in embryos of Iguana. In this animal he found in one case 

 three nerves distributed to the parieto-pineal organs : one 

 coming from behind and entering the epiphysis, and two 

 coming from right and left ganglion hebenula, respectively, 

 and entering the pineal eye. He found the right and left 

 nerves in three different embryos of Iguana eighteen days old. 

 In one case the nerve from the left ganglion hebenula was 

 nearly the same size as that from the right, but in the other 

 two individuals the left nerves were much reduced. It should 

 be added that Klinckowstrom has found the nerve to the pineal 



