No. 2.] THE HYPOPHYSIS OF AMIA. 501 
Sections of embryos corresponding in age to the fifth or 
hatching stage in the preceding article (Fig. 8), show the 
hypophysis (Fig. 4, hy.)? to have changed considerably in 
position. It now lies between the ventral wall of the infun- 
dibulum and the dorsal wall of the alimentary canal with its 
posterior end extending to a point some little distance ahead 
of the anterior end of the notochord (Fig. 4, n.), which 
reaches the postero-ventral region of the infundibulum. At 
this point the infundibulum presents a slight evagination (Fig. 
4, sv.), the fundament of the saccus vasculosus. The cavities 
first observed in the preceding stage are somewhat larger in 
this stage, and the cells, more columnar in form, are arranged 
apparently in a single layer around them, forming small vesi- 
cles (Fig. 4, c.). The ends of the cells next the cavities are 
clear, while their opposite ends contain numerous small gran- 
ules among which the nuclei are found. 
By comparing the position of the hypophysis in Figs. 3 and 
4, it seems to have migrated backward between the dorsal 
wall of the alimentary canal and infundibulum independently 
of surrounding parts. Mechanically, this change in position 
may be explained by supposing that the entire forebrain moves 
forward in its courses of development, its ventral wall thus 
passing over the hypophysis, and that later its infundibular 
region moves backward, due to the formation of the cerebral 
flexure, carrying the hypophysis with it. The first supposi- 
tion is supported by the fact that the large space between the 
anterior end of the forebrain and the ectoblast, seen in Fig. 3, 
disappears; the second by the fact that the saddle cleft is much 
narrower in Fig. 4 than in Fig. 3. 
The hypophysis in embryos about 22 mm. long is found to 
be located in the same relative position as in the preceding 
stage. It has, however, increased rapidly in size and has be- 
come broader and flatter than it was in the earlier stages. 
The vesicles (Fig. 5, c.) have increased in number and be- 
*The relative difference in size between Figs. 2, 3 and 4 is not due to a 
difference in magnification, as might be supposed, but to a difference in 
the actual size of the embryos, all being magnified 190 diameters. 
