158 



FREDERICK TILNEY AND LUTHER F. WARREN 



In the development of the pineal organ in all vertebrates, 

 only two of the germ layers play a part, i.e., the ectoderm and 

 the mesoderm. It is advantageous, therefore, in considering the 

 histological character of the pineal body, concerning which there 

 is much difference of opinion, to discuss the ectodermogenic 

 and mesodennogenic elements entering into that body. Of the 

 elements derived from the ectoderm the following have been 

 observed: 1) parenchymal cells, 2) ependymal cells, 3) neuroglial 

 cells, 4) ganglionie cells, and 5) nerve fibers. The following ele- 

 ments derived from the mesoderm have been described: 1) con- 

 nective tissue cells, 2) connective tissue Inibeculae, 3) blood 



