56 Journal of Comparative Neurology. 



ance of black tufts or little balls ; their nuclei are often invisi- 

 ble on account of the pigment. In the cells filled with pigment 

 little distinct round or oval bodies appear. In this case the black 

 color of the pigment disappears under strong magnification and 

 they are then of a dazzling whiteness. They give the impres- 

 sion of little sand grains. These are the elements of the white 

 pigment, if it may be so called. These pigment bodies are 

 found in the plasm of the cells. Only the nucleus may be with- 

 out pigment; sometimes they fill the cells entirely. At times 

 the inferior part (in the cylindrical cells) remains non-pig- 

 mented ; this occurs especially in the cells placed at the end of 

 the retina which are only half filled with pigment. 



Cavity of the pineal organ. In the youngest embryos the 

 cavity is in direct communication with the cerebral cavity; later 

 it is closed by the approach of the walls and only opens again 

 after some time. In the cavity of the organ there are two 

 kinds of structures ; a delicate framework and peculiar little vit- 

 reous bodies. These two structures occur in both Ammoccetes 

 and Petromyzon, but never at the same time, (i) The delicate 

 hyaline framework spread about in the cavity becomes yellow or 

 brown by the process of preparation. Its elements communi- 

 cate with the pellucida among whose cells they end, and also 

 with the retina where they are directly united with the sensitive 

 cells. In Petromyzon their union with the retina could not be 

 observed on account of the thickness of the pigment. They 

 were found in 5 specimens out of 17 in Ammoccetes. In some 

 preparations this coagulum was in the posterior part of the cav- 

 ity. In this case the anterior part was empty. The signifi- 

 cance of the union with the sensitive cells remains problematical. 

 (2) The little vitreous bodies of the second form are attached to 

 the interior of the cavity of the pineal organ, or they fill it en- 

 tirely. In the retina of adult Petromyzon these little bodies 

 were observed in connection with the cells of the organ. The 

 retina there was covered with vitreous bodies like little drops of 

 water. In some places these bodies were seen to arise directly 

 from the cylindrical cells. It seems that the vitreous mass 

 which these little bodies compose is secreted by the cells. In 



