ADULT PINEAL ORGAN OF BIRDS 297 



the external limiting membrane and mingling of the outer ends of the 

 ependymal cells with the fibres of the surrounding vascular connective 

 tissue, as is shown in Fig. 204, of a part of the wall of one of the follicles 

 in the epiphysis of an owl. This observation, which we owe to Studnicka, 

 is of great importance in the comparative study of the structure of the 

 pineal body in man and mammals, as it represents a stage in the late 

 foetal development which is paralleled in the development of the mam- 

 malian organ, and explains certain difficult points in the interpretation 

 of the appearances seen in the late foetal and post-natal stages of its growth 

 in the human subject. 



Fig. 204. — Section through a Part of the Wall of the Epiphysis of an Owl, 

 Strix flammea, showing Absence of an External limiting Membrane, 

 and Apparent Continuity of the Tapering Processes of the Outer 

 Ends of the Ependymal Cells, with the Fibres of the Supporting 

 Tissue. (After Studnicka.) 



bv. : blood-vessel. ct. : connective tissue. 



ep. : ependyma. 



The inner ends of the ependymal cells in this specimen, Fig. 204, 

 show the same rounded projections of protoplasmic material and thread- 

 like processes that are seen in the epiphyses of some fishes, Figs. 148, 154 ; 

 amphibia, p. 230 ; and reptiles, Fig. 178, p. 249 ; and there is the same 

 difference of opinion as to whether these projections are evidence of a 

 definite secretion or are simply due to degenerative changes in the cyto- 

 plasm and extrusion of effete material from the cell into the lumen of the 

 follicle. The contents of the follicles are very similar to those found in the 

 cavity of the epiphysis in fishes and reptiles, namely, a few detached 

 groups of cells either fused in a syncytium or separate, and thin coagula 

 containing cell-detritus such as are sometimes seen in the ventricles of 

 the brain. 



The structure of the adult epiphysis of birds, in spite of the resemblance 



