THE HYPOPHYSIS IN REPTILES 267 



embryos. An injected alligator shows no direct branches rom 

 the carotids to the hypophysis. However, the sinusoidal capil- 

 laries of the various parts are continuous, as is shown by various 

 injected specimens. A large venous channel, caudo-dorsal to the 

 hypophysis in lizards and snakes (fig. 41) apparently drains the 

 organ. Many veins are found in the connective tissue sur- 

 rounding the hypophysis in alligators. 



HISTOGENESIS OF THE HYPOPHYSIS 



The embryonic material used for this study was sectioned in 

 paraffin, the sections being from 5 to 10 micra thick. Various 

 stains were used and these are noted in the description, which 

 is based mainly on turtle material, with references to other 

 forms where necessary. 



In very young turtles (2.6 mm.) and snake embryos (3.3 mm. 

 Vipera verus) the hypophyseal evagination is composed of a 

 single layer of low columnar cells with a distinct basement mem- 

 brane. The cuticular border and cell membranes are distinct. 

 The large spherical nuclei, basal in position, contain one large 

 nucleolus, but very little other chromatin material, and have a 

 definite nuclear wall. 



The hypophysis in turtle embryos, 3 to 5 mm. in length, 

 has two or three rows of oval nuclei containing one or two large 

 round nucleoli and smaller chromatin masses. The latter are 

 peripheral in position and are sometimes connected by chromatin 

 strands with the eccentrically placed nucleoli. The cuticular 

 border and cell membranes are less distinct than in younger 

 embryos. On all sides, the pharyngeal roof is composed of one 

 layer of columnar cells with oval nuclei, although farther from 

 the hypophysis the cells are low columnar or cuboidal with 

 spherical nuclei. 



From three to five interlocking rows of centrally-placed nuclei 

 are found in the wall of the hypophysis of 7 to 9 mm. turtle 

 embryos (figs. 53 and 57). The nuclei are elongate and con- 

 tain a large nucleolus and a dense chromatin network. Thin 

 inner and outer cytoplasmic zones, staining darker than the 



