68 Journal of Comparative Neurology. 



terior vesicle finds abundant room in its primitive position at 

 the side of the stalk of the epiphysis. It is only in the early 

 stages in Teleosts, when the two vesicles are large relatively to 

 the brain and are nearly of a size, that crowding causes a par- 

 tial displacement of both vesicles into the median plane." 



A more plausible explanation, based upon the facts thus 

 far presented in both Teleosts and Amia, is that the anterior is 

 derived from the posterior and lies primitively in the median 

 plane, but as a direct result of the enlargement and forward 

 movement of the posterior it is crowded out of this plane and 

 comes to lie at the side of the posterior. 



The entire evidence thus far presented in Amphioxus, Pe- 

 tromyzon, Elasmobranchs, Teleosts and Ganoids indicates that, 

 although we have made great strides to show that the epiphy- 

 sial outgrowths are derived from segmental sense organs, we 

 have actually accomplished but little of the journey and we 

 find ourselves in the attitude of awaiting further research. 



