278 bulletin: museum of comparative zoology. 



a process (Stabchen). The fibrillae observable in these cells — which, he says, 



are undoubtedly neurofibriJlae in Apathy's sense — terminate in the Stabchen, 



and these terminations are to be regarded as the light-recipient elements of the 



visual cells. The clear axes of the pigment cells, seen in Haliotis and Helix, 



and held by Babuchin and by Carriere to be light-recipient elements, have no 



claim to that distinction ; they are the homologues of the sustentative elements 



— the glia fibres — of the nervous system, and the pigment cells themselves 



are the sustentative cells (ependyma) of the retina. The lens and vitreous 



body are the product of the pigment cells. 



It will be seen that conclusions arrived at by Dr. Smith in the present 



paper regarding the nature of the two kinds of cells composing the retina are 



in substantial agreement with those of Backer, and are the more worthy of 



consideration since they were arrived at quite independently of the earlier 



author's work. 



E. L. Mark. 

 Cambridge, February 16, 1906. 



