GROAVTH AND STRUCTURE OF HYPOPHYSIS IN RAT 345 



(neuroglia) cells, whose cytoplasm fades off into a very fine 

 intercellular network (neuroglia fibrils). The nuclei are rounded 

 distinct, and moderately chromatic. In some cases they appear 

 naked and nearly free from cytoplasm, which is the typical con- 

 dition from the age of one week onward. 



In later stages (3 weeks and above) the nuclei become pro- 

 gressively scattered, usually rounded or elliptical in form, and 

 vesicular in appearance, with average diameter of about 6 /x 

 (range 4 to 8 ju). The internuclear mass presents a fine plexus 

 of (neuroglia) fibrillae, interspersed apparently with a granular 

 matrix or ground substance. Among these granules there is 

 found a variable number of spherical masses, sometimes exceed- 

 ing the nuclei in size, and resembling 'colloid' in appearance. 

 They doubtless correspond to the colloid masses described by 

 Herring ('08) and Trautmann ('09) in the neural lobe of various 

 animals. 



The only change noted in the structure of the pars nervosa 

 during inanition (either in young or adults) is a variable degree 

 of hyperchromatism in the nuclei. In extreme cases, the nuclei 

 rarely become somewhat irregular, shrunken and pycnotic. No 

 definite change was observed in the internuclear mass, in the 

 fibrillae, granules or 'colloid' balls. 



h. Pars intermedia 



The pars intermedia (fig. 1) forms an epithelial plate sepa- 

 rating the pars nervosa from the residual lumen (hypophyseal 

 cavity). This plate is only a few cells thick in the central 

 region, but thicker peripherally. The cell boundaries are usually 

 indistinct. From the age of three weeks onward the cells of 

 the limiting layer (next to the lumen) are more or less flattened, 

 and rarety present small ciliated areas. 



In structure, the cells usually present cytoplasm filled with 

 fine, pale violet granules, resembling those of the faintly baso- 

 philic cells of the pars anterior. The nuclei are round or oval, 

 and moderately chromatic. Hyperchromatic and even pycnotic 

 nuclei are occasionally found, but are rare in the normal animals. 

 They are mentioned by Stendell ('14) as of uncertain significance. 



