F. S. CONANT ON THE CUBOMEDUS^. 49 



a. There is not good evidence of an alternation of cone-shaped pig- 

 ment cells. and spindle-shaped visual cells, with the nuclei of the latter at 

 a lower level than those of the former. 



b. From some of the retinal cells otherwise not distinguished, there 

 extend rod-like processes into the vitreous body, such as described by 

 Schewiakoff. 



c. The cone-shaped streaks of pigment in the vitreous body belong 

 to the underlying pigment cells, in fact are direct continuations of them, 

 and at their distal ends they are prolonged into fibrous processes lying 

 in canals of the vitreous body exactly like the visual fibres of Schewi- 

 akoff. 



d. The vitreous body is not a homogeneous secretion, but is com- 

 posed of prisms of refracting substance, each with a denser central fibre. 



Let us go over these four points in detail. 



(a) As to the first, the question whether there is an alternation of 

 pigment and visual cells, I am not prepared as yet to make a positive 

 statement, since my not seeing both kinds as they are described has 

 little evidential value against the fact that Glaus and Schewiakoff both 

 claim to have seen them. Perhaps proof could be obtained one way or 

 the other by maceration of fresh or of specially prepared material, 

 which none of us had. My evidence for not confirming alternation rests 

 wholly upon sections. Fig. 58 represents a radial section through part 

 of the larger eye of Charybdea, made from an osmic preparation which 

 in this case showed two advantages over the material fixed in corrosive- 

 acetic (usually by all odds the best), namely, that the vitreous body (vb) 

 was not shrunken away from the retinal cells, as almost invariably 

 happens, and that the retinal cells were contracted apart from one 

 another in some places in such a way as to be almost equal to a macer- 

 ated preparation. Now, in the figure it is seen that there is an apparent 

 alternation of two kinds of cells, more regular than I usually find, but 

 the ones that are undoubtedly the pigment cells of Schewiakoff are the 

 ones that show the fibrous processes like his visual cells, and the pigment 

 streaks in the vitreous body are seen to be integral parts of the cells, not 

 cone-shaped masses lying in the vitreous body, merely associated with 

 the pigment cells. If these are the pigment cells of Schewiakoff, the 

 shorter cells in between must be his visual cells, yet they can by no 

 means be said to conform to a spindle-shaped type, nor are their nuclei 

 always at a lower level than (that is, internal to) those of the pigment 

 cells. If the long cells with the fibres are, on the other hand, considered 

 7 



