j6 THE PINEAL ORGAN 



surface of the head, which appears before the development of the feather- 

 papilla;, opposite the point towards which the apex of the pineal diverti- 

 culum is directed. The epidermis is raised above the level of the sur- 

 rounding skin. In this situation there appears at the same time a remark- 

 able accumulation of pigment, both in the epidermis and the subcutaneous 

 mesenchyme. The cupola-like projection later divides into two small 

 hillocks. Still later, the parietal spot becomes surrounded by a circle 

 of feather-papillae. Finally, the area is invaded by the ingrowth of small 

 feather-papillae and it eventually disappears. Studnicka, in commenting 

 on these observations, mentions that he has himself heard of a case in 

 which a parietal foramen was present in the skull of an adult goose, and 

 that a round hole closed by connective tissue is found in the roof of the 

 skull of adult geese, more especially in those varieties which possess a crest. 

 This hole lies just in front of the point where the epiphysis ends, and he 

 states that it can have no other significance than that of a parietal foramen. 

 The occasional appearance of this embryonic vestige in the above- 

 mentioned varieties of sea-gull and allied species of bird and of the 

 parietal foramen in the skull of adult geese is especially interesting as the 

 parietal foramen is usually absent in the skulls of birds, notwithstanding 

 the high degree of development of the pineal body. The pigment spot 

 and the occasional presence of a parietal foramen in these birds serve as 

 an indication of the previous existence of a parietal sense-organ in the 

 ancestors of birds and of the identity of the avian epiphysis, or proximal 

 part of the pineal apparatus, with the more fully evolved organ which is 

 present in certain living reptiles, such as Varanus and Sphenodon. 



Pigmentation of the Pineal Organ in Mammals 



We have already referred to the work of Quast, p. 62, on the pigment 

 of the human pineal organ. All authors appear to be agreed that in the 

 mammalian pineal organ pigment is contained in two types of cell : 

 (1) the parenchyma cells, (2) branched or elongated cells which are 

 present in abundance in the capsule and interlobar septa following the 

 course of the vessels. The latter often appear to be stretched out over 

 the vessel walls and to lie in the perivascular spaces. There is, however, 

 considerable difference of opinion with respect to the colour of the pig- 

 ment granules in the two types of cell, and it seems probable that consider- 

 able variations occur in the depth of colour between pale yellow and 

 dark brown, or even black, which are due in part to age and in part to 

 different methods of preparation. The close association of the branched 

 or elongated pigment cells with the blood-vessels, which is especially 

 evident in the horse, has given rise to the opinion that the situation of the 



