259 

 The Americas Ixdian. His Relioion. By GEORfTE L. Curtis. 



JsOTES ox THE ORIGIN OF THE EPIPHYSIS CEREBRI IN" AmIA. By B. M. DaVIS. 



[Abstract.] 



The presence of the epiphy.iis in all the vertel)rate3 from the Cyclostomes up 

 has made it an object of study among comparative anatomists for a long time. 

 Its structure and development has been described for all the groups except the 

 Ganoids. 



I have had occasion lately (together with Dr. Eyclescheimer of Chicago Uni- 

 versity) to examine the early development of this structure in Amia calva, and 

 this is merely a preliminary note to a more detailed and complete account, which 

 will be published later. 



It has been described {e. g., Hertwig's Embryology) as always arising in 

 exactly the same way, i. e., as a forward evagination of the roof of the thalameu- 

 cephalon. As a matter of fact, however, the opposite is true in several forms. 

 {Petromyzon, Acipenser, Amia, Chick.) 



Its first appearance in Amia is in a larva still uncoiled from the yolk. It is 

 noteworthy that it does not appear this early in all individuals. In some cases it 

 does not develop until the larva has uncoiled from the yolk and has attained a 

 length of four or five millimetres. 



It is at first a simple fold in the brain-roof directed backward. There are no 

 histological features which would distinguish it from the adjacent parts of the 

 brain. 



The stages immediately succeeding this show a gradual change in structure. 

 The upper part of the fold is differentiated into the epiphi/.iis. It is a glove-finger- 

 like structure, with its cavity bounded above by two rows of cells and below by 

 several. 



The distal end for some time remains much the same in structure, but the 

 dorsal wall of the proximal end becomes thickened. This thickened portion 

 extends forward and becomes the so-called "anterior vesicle." From the time of 

 origin it would seem that "secondary vesicle" would be a better designation. 



The two vesicles are attached to the brain-roof by a stalk and have a common 

 opening into the thalamencoele. 



Later the anterior or secondary vesicle shifts to the left, and from the ten- 

 millimetre stage on is found to the left of the primary vesicle. 



