266 H. E. JORDAN 



CONCLUSIONS AND DISCUSSION 



The pineal bod}^ of the sheep undergoes its greatest development 

 (five-fold) during the first year of life. After this period regres- 

 sive changes make their appearance. Its general structure (i.e., 

 lobulation, connective tissue framework, arrangement of paren- 

 chyma into follicles, presence of blind alveoli, large peri-vascular 

 lymph spaces, great vascularity, and presence of granules in the 

 cytoplasm), indicates a glandular function of the nature of elaborat- 

 ing an internal secretion. The coincidence of greatest develop- 

 mental activity with greatest body growth and the appearance of 

 sexual maturity indicates a casual nexus. However, there is no 

 cytologic evidence in support of this opinion. The parenchymal 

 cells are all of one type : more or less highly differentiated ependy- 

 mal cells, giving origin to neuroglia cells and fibers, and inter- 

 neuroglia cells (figs. 8, 10, and 11). The cytoplasmic granules 

 are evidently melanic and represent the morphological expression 

 of a hereditary impulse to function as their ancestral homologues 

 in the median visual organ, the parietal eye. 



A priori, one inclines to believe that so well developed and large 

 a structure, compared with the brain of sheep, must have a specific 

 and important physiologic function. But the histologic evidence 

 in confirmation of this impression is almost nil. The effects of 

 intra- venous injections of pineal extract are definite, but hardly 

 pronounced or specific enough to have vital significance. Of 

 course, the assumed specific internal secretion might indirectly 

 affect the body metabolism and so be highly important for health 

 and normal growth. This matter can only be fully elucidated by 

 extirpation experiments. The only significant fact from the 

 standpoint of function revealed by the developmental history of 

 the pineal body in the sheep is that, whatever possible function 

 it may have in the animal economy, this is most active during 

 the first eight months of post-natal life. 



It remains to discuss the fate of the numerous cysts of the sec- 

 ond half of the foetal stage of development. Their abundant 

 presence makes particularly striking the similarity between the 

 pineal body of this stage and an alveolar gland. Their disappear- 



