66 P RATHER. [VOL. I. 



In a larva about fourteen days old a median sagittal section 

 (Fig. 11) shows marked changes in surrounding parts, with but 

 little change in the hypophysis. The saccus vasculosus has 

 grown until it measures at this stage 120 /A in length, and from 

 6 //, in width at its point of origin to 27 /x at its widest part. Its 

 tip now touches the base of the hind brain. The columnar 

 cells which characterized it in the preceding stage are yet very 

 noticeable, the transition to the rounder cells of the infundib- 

 ular wall above being very abrupt, while the transition to the 

 cells of the infundibular base is more gradual. Beneath, the 

 hypophysis rests directly upon a strand of fibrous tissue (ins.} 

 continuous before and behind with the perichondrium surround- 

 ing the sphenoidal cartilages, which are encroaching from all 

 sides. The membrane roofing the mouth (em.} has become 

 widely separated from the hypophysis, and in it dental protu- 

 berances and glandular cells have differentiated. The hypoph- 

 ysis has now attained a size of 156/4 by 56 /*, and has several 

 small spherical or lenticular cavities which do not com- 

 municate. 



A sagittal section of the hypophysis of a larva about the 

 same age is shown in Fig. 12 strongly magnified. It will be 

 seen that a few mesodermal cells have come to lie between the 

 hypophysis and the brain, forming a thin layer separating the 

 two organs. With this interpolation of mesoblastic tissue the lob- 

 ing of the hypophysis begins, and this continues to increase 

 with age. A large central oval lumen is conspicuous at every 

 stage, while in the section here figured, several smaller lumina 

 are met with as one examines the sections of the series. The 

 principal lumen in this case measures 19/4 by 6 /x, and can be 

 detected in but two sections, showing that its shape is lenticu- 

 lar. The smaller ones are more nearly spherical, and each is 

 found in but a single section. No communication between 

 them can be found. The hypophysis in this larva measures 

 164 /A in length by 57/* in thickness. The characteristic radiate 

 arrangement of the cells about the lumina is very noticeable. 



Fig. 1 3 shows the relations of the hypophysis to surrounding 

 parts, at a stage about one day older, in a transverse section 

 through the middle of the organ. The oral epithelium has 



