F. S. CONANT ON THE CUBOMEDUS^E. 47 



that two similar ones would appear on the other side, since the four 

 simple eyes are symmetrically paired on either side of the mid-line. The 

 sketch seems to show at least this much, that even in the living state the 

 lens of the larger eye projects out beyond the other contours of the 

 surface, so that the marked convexity ascribed to it in descriptions is not 

 to be attributed to the preservation. 



It is in reference to the structure of the retina and vitreous body of 

 the complex eyes that I have found myself unable to come to the same 

 conclusions as Claus and Schewiakoff . Since the work of the latter goes 

 much further into the detail of the subject than does Claus's paper, it 

 will be sufficient for me to compare my results simply with those of 

 Schewiakoff. 



The latter finds that the retina is composed of two kinds of cells, 

 corresponding to the supporting and sensory cells referred to in the 

 description of the nerve ring. These he figures ('89, Taf. II, Figs. 12 and 

 13) as alternating regularly. The two kinds of cells differ as follows : 



(1) Shape. The supporting cells like those referred to before, are 

 cone-shaped, having a proximal fibrous process that runs into the under- 

 lying stratum of nerve fibres, and on the surface of the retina a broad 

 distal pigmented termination. The sensory cells are spindle-shaped, the 

 proximal processes becoming continuous with fibres of the underlying 

 nervous mass, while the distal process runs up to the surface of the 

 retina (the part toward the lens) in between the ends of the supporting 

 cell. The two kinds of cells are accordingly designated as pigment and 

 visual. 



(2) Position of nucleus. This comes in as a corollary of the shape. 

 The nuclei of the visual cells lie in the enlarged central part of the 

 spindle-shape, and, therefore, at a lower level than the nuclei of the 

 alternating pigment cells. 



(3) Processes in the vitreous body. The distal processes of the spindle- 

 shaped visual cells are continued through the vitreous body to the cells 

 of the lens as rod-like visual fibres which lie in canals in the (supposedly) 

 homogeneous vitreous body. The pigment cells on the other hand have 

 no fibres passing from them through the vitreous body, but in the latter 

 are situated cone-shaped masses of pigment whose bases rest upon the 

 broad ends of the pigment cells without, however, being a part of the 

 cell. 



(4) Pigment. The distal ends of the pigment cells in the retina are 

 strongly pigmented, as the name implies. The processes of the visual 



