38 Journal of Comparative Neurology. 



in all craniota in a more reduced state ; the cephalic is the 

 " second epiphysial vesicle " in Petromyson, , the parapineal or- 

 gan of Studnicka ('95). It occurs in embryo teleosts and Ainia 

 (Hill), and in reptiles becomes separated from the brain as the 

 well known parietal eye of lizards. There is, however, no case 

 so far as known to me where they might not be interpreted as 

 but modified parts of the same primary evagination,^ were it 

 not for the observation of Locy of three pairs of depressions 

 upon the medullary plate of the shark embryo ; the first enter 

 the optic evaginations ; the second he traced to the epiphysis ; 

 while the third pair was lost. 



As has been said by others, the need now is the accumula- 

 tion of facts showing the relations in this region of the brain in a 

 wide range of forms, especially embryologic data which will 

 throw light on the first appearance of these (or this) evaginations 

 in the various forms. It is as contributing a little to the interpre- 

 tation of these structures tiiat the following is offered. It has 

 just been stated that Hill has already described the existence of 

 two epiphysial structures in the embryo Aniia. The cephalic 

 evagination (epiphysis I) in embryos of 10 mm. length is an 

 elHpsoid sack lying upon the left side of the epiphysial stalk 

 (epiphysis II) ; its cavity is connected with the cavity of the 

 brain. Likewise in 13 mm. Amia the cavity is in communica- 

 tion with the brain, but in embryos 1 5 mm. long the connection 

 is severed and epiphysis I lies upon the left side of epiphysis II. 

 It appears that the adult or later embryos were not examined. 

 In Sahno (the teleost more especially studied ; others were 

 Catostoimis, Stizostedion and Lepomis) the connection is severed 

 in 13 mm. embryos ; in 25 mm. Salmo (160 days old) the cav- 

 ity is obliterated and in 2 year fish it is recognizable only in 



' Leydig, Beraneck and Francotte state that two distinct outgrowths from 

 the roof of the diencephal in reptiles occur. Klinckostrom, Selenka and Soren- 

 sen however think there is but one evagination. Accessory parietal eyes which ■^ 

 have been observed in certain lizards appear variable in number and cannot yet 

 be interpreted. Likewise in Petromyzoti, earlier stages of the development of 

 these structures are wanting and the cephalic vesicle may prove, as believed by 

 some, to be derived from the caudal. 



