Evci.eshymer-Davis, Epiphysis and Paraphysis in Amia. 5 3 



even at this comparatively late stage there is as yet no trace of 

 a lumen in the secondary vesicle. 



Paraphysis. The paraphysis has grown in length and has 

 assumed the form of a vesicle. It extends farther forward than 

 in the earlier stage. Histologically its walls show the same 

 characteristics noted in the preceding stage, consisting of a sin- 

 gle layer of thickened columnar epithelium. Its posterior wall 

 possesses considerable pigment whiie its anterior and dorsal 

 walls seem to possess little or none. 



Lan'a ig-20 days, 12-1^ mm. 



Fig. 27 is an outline of the roof of the third ventricle 

 showing the position and relative size of the epiphysis. Fig. 

 28 represents an enlarged section through the epiphysial region. 

 When compared with the preceding stage certain changes are 

 observed. The vesicle extends farther forward and is com- 

 pressed dorso-ventrally. The superior commissure {sc.^ has 

 been crowded farther into the third ventricle. The roof of the 

 third ventricle just anterior to the commissure is much thinner 

 than in the preceding stage. 



In this stage we have noticed for the first time a peculiar 

 tract (/"/,) lying in the ventral portion of the primary vesicle, 

 which, from its similarity to the commissure lying immediately 

 below, we interpret as a fiber tract. The relative positions of 

 the vesicles are well shown in the series of transverse sections 29, 

 30, 31, 32 taken along the lines bearing their respective num- 

 bers in Fig. 28. Fig. 30 shows that the overgrowth of the pri- 

 mary over the secondary has progressed beyond the condition 

 shown in Figs. 20, and 25 of the preceding stages. In Fig. 31 

 the tract (/?.) already noticed in the sagittal section (Fig. 28) 

 is well defined. It lies in close contact with the superior 

 commissure {sc.^. 



In some of our sections of this stage we have not been 

 able to show the existence of nerve fibers passing from either 

 the superior or posterior commissures into this tract. In one 

 series however, we have been able to trace, beyond any shad- 

 ow of doubt, nerve fibers passing directly from the superior 



