186 FREDERICK TILNEY AND LUTHER F. WARREN 



both because of their tendency to be collected into well-defined 

 groups, as well as the unusual dimensions of their cytoplasm. 

 Here, as in none of the other forms already described, does the 

 character of the pineal cell stand out. Not only is it much 

 larger, but it has the granular appearance so notable in the 

 human pineal cell. The large cells with the faintly staining 

 nuclei are found scattered among the cells just mentioned and 

 also scattered diffusely throughout the organ. The small cells 

 are less prominent, although both types may be recognized. 

 The cells are arranged according to an apparent design, although 

 the large pineal cells group themselves in irregular masses. 

 No tendency to cord formation is, however, observed. There 

 is a rich and delicate network of connective tissue, and many 

 capillaries surround the cell masses. No concretions were 

 observed (fig. 89). 



7. Homo sapiens. In the adult human pineal body the types 

 of cells already described as present in the epiphysis of other 

 mammals may be observed here also. The large cells with 

 granular cytoplasm and large deeply staining nuclei are the 

 most prominent elements. They are arranged in regular masses 

 very similar to those observed in Simia saiyrus, although the 

 intervening areas are less extensive, so that in man the cell 

 masses seem to run into each other without sharp line of demar- 

 cation. A very dense network of connective-tissue trabeculae 

 forms the frame work of the organ, while the vascularity of the 

 structure is richer than that of any other form observed. Con- 

 cretions of varying sizes are present throughout the entire 

 gland (fig. 90). 



The histogenesis of the pineal gland was studied in the cat 

 and human. The inception of differentiation in the cat presents 

 itself as a marked thickening in the walls of the more caudal of 

 the two evaginations. In the 70 mm. cat this thickening is so 

 pronounced that the recess in the anlage is reduced to a narrow 

 lumen. The cells multiply at the caudal extremity of the now 

 almost solid epiphysis. From the stage of 120 mm. to term a 

 process of diverticular formation occurs. This starts at the 

 base of the gland at its attachment to the roof -plate and grad- 



