GROAVTH AND STRUCTURE OF HYPOPHYSIS IN RAT 347 



in the amount or structure of the colloid (either in the cavity or 

 in the pars nervosa) were observed in the rats subjected to 

 inanition. 



c. Para anterior {disialis) 



The parenchyma cells of the pars anterior present the well 

 known types (figs. 2 and 4). These have been classified in 

 various ways, the most useful for present purposes perhaps 

 being that of Trautmann ('09). He recognizes the following 

 classes of cells: (1) acidophilic (strongly or weakly); (2) baso- 

 philic (strongly or weakly); (3) chromophobic. The nmnber, 

 arrangement and structure of these cell-varieties differ consid- 

 erably in different species; and, at least in the rat, in different 

 individuals. 



The chromophobes form an undifferentiated type of cell, 

 relatively numerous in the newborn rat, but somewhat rare 

 after the third week. The weakly basophilic type is usually 

 the most numerous, the strongly basophilic rare. The acido- 

 philic (eosinophilic) type is evident in the newborn and at three 

 weeks, though much better differentiated later. It usually forms 

 at least one-third of the total nmnber of cells. The weakly 

 acidophilic are more numerous than the strongly acidophilic, 

 though it would be hard to draw the line between them. In fact, 

 there appear to be numerous transition forms between all varie- 

 ties (especially the chromophobic and weakly basophilic). 



Tilney ('11) describes the basophiles as occupying the pe- 

 riphery, and the acidophiles the central region. I do not find 

 any constant arrangement of this sort. The acidophiles are 

 usually scattered throughout the lobe, either singly or in small 

 groups, interspersed with basophiles. Sometimes, however, 

 either basophiles or acidophiles may predominate in the pe- 

 riphery. 



In the normal gland, the cytoplasm of the chromophobic cells 

 is very small in amount, sparsely granular, and faintly staining 

 (fig. 2). In the basophilic and acidophilic typc^s, the cyto- 

 plasm is more abundant and usually finely' (sometunes coarsely) 

 granular in appearance. In the strongly chromophilic cells, 



