28 E. R. HOSKINS AND M. M. HOSKINS 



the male hypophysis is often larger than that of the female 

 of the same size, so that our first findings were the result of chance 

 variation. From our recent observations it is evident that there 

 is considerable variability in the size of the hypophysis and no 

 constant size difference between the sexes exists. 



Microscopic structure. The three lobes of the hypophysis are 

 well shown in the figures 56 to 59. In smaller larvae the three 

 lobes consist of closely packed undifferentiated cells irregularly 

 round with granular cytoplasm and containing nuclei of corre- 

 sponding shape. This condition is retained normally until 

 nearly the time of metamorphosis (fig. 56). At the time of 

 metamorphosis the cells of the inferior lobe have usually begun 

 to form cords which are separated by connective tissue (figs. 

 57 and 59), but the gland in some other cases is still undiffer- 

 entiated even after metamorphosis (fig. 60). 



In larger thyroidless larvae at the time of metamorphosis of 

 the controls the inferior lobe (fig. 58) has already been divided 

 into cords, but the other two lobes are not differentiated. The 

 gland is relatively larger in these thyroidless specimens than 

 in the controls of the same age, and most of the hypertrophy 

 is confined to the inferior lobe. After cords form in the inferior 

 lobe there are found two kinds of cells there. One is of the un- 

 differentiated type described above and the other is somewhat 

 columnar with cytoplasm finely granular and eosinophilic and 

 containing a round or oval darkly staining nucleus. A few of 

 these eosinophilic cells are found in the controls just before 

 metamorphosis and a larger number in the thyroidless larvae 

 of the same age (figs. 61 and 62). At this time the anterior 

 and superior lobes consist of cells of indefinite shape (figs. 61 

 and 62). 



In older thyroidless larvae (fig. 63) the inferior lobe of the 

 hypophysis contains a larger percentage of eosinophilic cells than 

 it does in younger larvae. Most of these cells are irregular in 

 shape, but some are columnar. Their cytoplasm is often so 

 nearly homogeneous as to have the appearance of colloid. The 

 non-eosinophilic (chief) cells are much more abundant than those 

 of the eosinophilic type. In these older larvae the cells of the 



