THE PINEAL BODY OF THE SHEEP 267 



ance in large part during early post-natal stages (very few remain 

 at 8 months) indicates that the assumed glandular activity pre- 

 vails only during foetal life. These 'acini' are filled with coagu- 

 lated fluid, which may possibly be of the nature of an internal 

 secretion. However, their origin as above described, shows that 

 they are actually of the nature of cysts, and make it very improb- 

 aole that their fluid content has secretory value. Contrary to 

 Flesch's opinion (cited from Studnicka) they are not lined with 

 ependymal cells from the recessus supra-pinealis, nor have the 

 lining cells a distinct basement membrane. The disappearance 

 of these numerous ' acini' is accompanied by the more active pro- 

 liferation of post-natal life obliterating the space by simple pres- 

 sure on the surrounding cells. Proliferation of cells in the actual 

 wall of these acini is a minor contributory factor in their obliter- 

 ation. Since these acini arise as cysts (i.e., independently of recess 

 or surface) in a healthy and actively growing structure, and dis- 

 appears again in large measure when the pineal body attains its 

 greatest bulk, their significance in terms of function is very obscure. 

 They become more intelligible when viewed from the phylogenetic 

 standpoint. Th'ey may be interpreted as ontogenetic representa- 

 tive of true alveoli in the glands of phylogenetically earlier 

 ancestors. 



Finally, it seems important again to emphasize the fact of a 

 close structural similarity (practical identity) between the pineal 

 bodies of late foetal (4f months) and early post-foetal life (to 8 

 months) ; also the uniformity in size, form and texture of the pineal 

 bodies of young sheep (first year), and the considerable variation, 

 both local and general, among the pineal bodies of older sheep. 

 The variations designated indicate degeneration and the abate- 

 ment of any possible active function. 



SUMMARY 



1. The pineal body of the sheep begins its development as in 

 other forms as an evagination from the roof of the diencephalon. 

 At the 2.5 cm. stage of development it has the form of a definite 

 pocket lined with ependyma thickened apically. 



