No. 2.] THE HYPOPHYSIS OF AMIA CALl'.L 6j 



further differentiated. The lateral cartilages (j/-.) of the skull 

 are closely encroaching from the sides, enclosing the internal 

 carotids (bv}. These cartilages are connected by a strand of 

 the perichondrial membrane which runs beneath the hypophysis. 

 The organ is almost perfectly lenticular in cross-section, meas- 

 uring iSo/u, by 70 /x. A principal lumen is seen in the center, 

 but others are found at other positions in sections in front and 

 back of this one. 



In a larva between twenty-two and twenty-six days old, a cross- 

 section (Fig. 14) shows the hypophysis appreciably enlarged, 

 measuring now 220 /JL by 75 /u. An irregular but distinct lobing 

 may be seen, more pronounced on the upper than on the lower 

 side. In this way, from a very symmetrical organ in the fifteen- 

 days stage, we get here a marked asymmetry. It is here firmly 

 adherent to the infundibulum, but quite apart from the wall of 

 the cranial cavity. This separation from the base of the cranial 

 cavity may be considered an artificial condition, as succeeding 

 stages invariably show it to be in contact with this wall. The 

 distinct upward bend in the infundibular base, the enlargement 

 and gradual encroachment of the lateral cartilages, and the 

 advancing differentiation of organs in the oral epithelium may 

 be remarked. 



The same section of the hypophysis highly magnified (Fig. 

 15) shows its histological structure to present some interesting 

 features. The large central lumen with its very definite lining 

 membrane is a striking object. It is ovoid, measuring 24 JM by 

 14^1. Other spheroidal but smaller lumina are to be found 

 near the tip of the different lobes as they are traced by sections, 

 but communication of these lumina with each other, or with 

 the central lumen, cannot be definitely proved. It seems that 

 communication may be had through very narrow channels repre- 

 senting connected intercellular spaces between rather definite 

 rows of cells and running from the lumina of the lobes towards 

 the central lumen. But apparently these channels are closed 

 before reaching the lumen. Such spaces may be seen in the 

 figure (si.} running out into the lobes to the right and to the 

 left. It will be noticed that the cells maintain a rather definite 

 and orderly arrangement about the central lumen. There is a 



