3l6 THE PINEAL ORGAN 



in human foetuses from 5! months to the time of birth, and of 18 infants 

 in the first month of post-natal life, during which critical period con- 

 siderable changes in structure occur which have been described by these 

 authors and also by Krabbe. Globus and Silbert have also described the 

 pineal organ of children varying in age from 2 months to 5 -J- years and of 

 older persons up to the age of 72 years. They distinguish two principal 

 types of cell-elements, namely, small cells with deeply stained oval 

 nuclei and larger cells with more abundant protoplasm and pale vesicular 

 nuclei. The latter, more especially during the first two months of post- 

 natal life, occupy the central zones of lobular areas, which are bounded 

 externally by the small dark cells. These rounded or polygonal areas 

 appear to form structural units of a system which on section has a mosaic- 

 like appearance. About the beginning of the 2nd month of post-natal 

 life the mosaic appearance becomes less pronounced, and from this 

 time up to the 10th month these authors believe that a transformation 

 takes place of the small dark cells into fibroblasts. Krabbe, on the other 

 hand, holds the view that the small, darkly staining cells, which he calls 

 " proparenchyma cells," undergo a metamorphosis during the first year 

 of post-natal life, which is usually completed by the end of the first year. 

 The small proparenchymatous cells give rise to large cells with clear 

 vesicular nuclei ; these are the " parenchymatous cells," and he believes 

 that the fibrous elements are derived entirely from the connective tissue. 

 Most authors agree with Krabbe in assigning the origin of the fibrous 

 connective tissue to the ingrowth of mesoderm, which accompanies the 

 penetration of vessels between the outgrowing buds of epithelium, and 

 they believe that the parenchyma cells originate by transformation of the 

 small darkly stained cells of which the epithelial outgrowths are primarily 

 composed ; but it seems probable that the transformation of the indifferent 

 epithelial cells into the large round cells with pale nuclei commences at 

 a much earlier period than the post-natal, namely, about the middle of 

 foetal life, and that it only becomes a pronounced feature during the 

 critical period of early infancy (1st to 2nd month). It is also generally 

 believed that the small round cells give rise to a certain number of glial 

 cells in addition to the parenchymal cells which in young subjects form 

 the bulk of the tissues composing the pineal organ ; but they do not 

 give origin to fibroblasts, these being wholly derived from the ingrowth 

 of mesodermal tissue. 



Later, a still further development takes place of the larger round 

 cells, with clear vesicular nuclei, namely, the outgrowth of the character- 

 istic processes of the parenchyma cells (see Fig. 218) ; and according to 

 Dimitrowa and others the appearance of what they believe to be " secre- 

 tory " granules in the nucleus and in the cytoplasm of these cells (Fig. 219). 



