DEVELOPMENT OF THE HYPOPHYSIS 441 
Fig. 42 Transverse section of the hypophyseal stalk of a 37 mm. prabeya 
(H.E.C. Series 363). X 350. 
Fig. 43 Transverse section of the hypophyseal stalk of a 41.5 mm. embryo. 
(H.E.C. Series 369). xX 350. 
is low columnar in type (fig. 40); the inner is irregular and the 
nuclei are oval in outline but not regularly placed. Figure 40 
is of a section through approximately the middle of the stalk. 
The lumen and stalk are larger where it connects with the hy- 
pophysis and with the mouth, both ends being funnel-shaped and 
joined by a narrower middle part. The connective tissue around 
the stalk is mesenchymal in character. Immediately around the 
stalk the cells are concentrically arranged. This character is 
more pronounced in later stages. 
In a 33 mm. embryo the two ends of the stalk are funnel- 
shaped, as before, and contain a lumen, while the middle part of 
the stalk is made up of a mass of cells in which no lumen is present 
(fig. 41). The outer layer of cells, though still definite at the 
ends, is no longer so in the middle part. The nuclei are more 
spherical in shape and contain a denser chromatin network. 
The arrangement of the mesenchymal cells around the stalk is 
concentric. 
In a 37 mm. embryo the stalk is greatly reduced in size. The 
nuclei are massed in the center and are surrounded by a densely 
staining cytoplasm (fig. 42). Some pigment is scattered through- 
out the stalk, as in all of the specimens. The concentric arrange- 
ment of connective tissue cells is more marked. 
In some embryos 40 mm. in length no remnant of the stalk is 
found. In a 41.5 mm. embryo a small elongated densely stain- 
