140 Herring 



and appears to be the result of proliferation of the epithelium at the 

 end of the cleft, a lumen being retained in the outgrowths continuous 

 with the original cavity. 



In the dog large vesicles are frequently seen in the epithelium ; they 

 are larger than those of the cat's pituitary, and often occur in groups. 

 They are for the most part deeply situated and often separated from 

 the nervous substance by a single layer of flattened cells, and even these 

 may be deficient, so that the colloid material is partly bordered by the 

 nervous substance. In the monkey the vesicles are less numerous, and 

 occur for the most part in the epithelium at the ends of the cleft. 



The cells which make up the greater part of the epithelial border are 

 well-defined polygonal cells resembling somewhat the clear cells of the 



Fig. 9. — Vertical section througli e])itlielial investment and nervous substance of posterior lobe 

 of new-born kitten. Prepared by Cajal's method. 



The epithelial investment contains numerous spinille-shaped cells, the marginal cells of Retzius ; the nervous 

 substance is composed of neuroglia cells and granular-looking matrix. Numerous blood capillaries are 

 found in the nervous substance, but do not penetrate into the epithelium. 



anterior lobe, but they stain rather more deeply and their protoplasm is 

 more granular. Occasionally deeply-staining cells are met with, but they 

 never show the eosinophil granules of the cells of the anterior lobe. The 

 colloid material appears to be a product of the epithelial cells, and 

 accumulates between adjacent cells, giving rise to the appearances of 

 vesicles. The spaces thus formed may communicate, but are for the 

 most part closed. 



The epithelial investment of the posterior lobe presents another notable 

 feature which distinguishes it from the remainder of the epithelial part of 

 the pituitary^ — it rarely contains blood-vessels. In the pituitary of the 

 cat no vessels occur in the thinner portions, and where the epithelium is 

 much thickened a few capillaries only enter it from the adjacent nervous 

 substance. Large blood-vessels, chiefly veins, and capillaries are very 



