94 BULLETIN OF THE 



Serolis before the formation of the rhabdome proper is rather in favor 

 of my interpretation than opposed to it. The direct evidence that the 

 axial body is a proximal extension of the cone cells is not as conclusive 

 as could be desired. The condition which most favors this view is as 

 follows. In longitudinal and transverse sections of the ommatidia, both 

 in adult and embryonic specimens, no line of separation has been observed 

 between the protoplasm at the deep end of the cone and the substance 

 which occupies the axial part of the ommatidium proximal to the cone 

 (compare Fig. 65). In attempting to determine the true relation, it is 

 important to keep clearly in mind the fact that the proximal end of the 

 cone, usually bounded by a sharply marked line, is not the proximal end 

 of the cone cells ; but; as Watase ('9(3, Plate XXIX. Fig. 1) lias well shown, 

 the cone is surrounded proximally as well as laterally by the protoplasmic 

 material of its cells. It is this material, not that of the cone proper, 

 which forms the proximal elongation. 



I had hoped that by isolating the elements of the retina I could ob- 

 tain more conclusive evidence of the connection of these parts, but my 

 efforts were of no avail. My ill success was due, I believe, not to any 

 want of connection between the structures treated, but to the fact that 

 the material at my disposal had been kept so long in strong alcohol that 

 it had become unfit to serve for isolation. This conclusion seems to me 

 to be confirmed by the fact that I was unable even to isolate satisfac- 

 torily the retinuhe, structures which are usually separable with ease in 

 the fresh retinas of most Crustaceans. 



If the view which I have set forth in the foregoing paragraphs con- 

 cerning the interpretation to be put upon the axial part of the so called 

 rhabdome of Serolis be correct, it follows that the true rhabdome of this 

 Crustacean must be considered as composed of four rhabdomeres, each 

 of which is applied to the axial face of its appropriate retinular cell, 

 and that these four rhabdomes are prevented from uniting with one 

 another by a proximal extension of the cone cells which occupies the 

 axis of the ommatidium from the cone to the basement membrane. 



Beddard ('84% p. 21), in bis account of the eye in S. Schythei, states 

 that the cone is " enclosed in a sheath of deep black pigment cells," and 

 Watase ('90, p. 294) has observed that in tins genus there are two such 

 cells for each ommatidium. I believe that the number has been given 

 correctly, fir although I have not satisfactorily isolated the cells, I feel 

 confident that I have identified their nuclei, and the number of these is 

 twice that of the ommatidia. 



The nuclei of these pigment cells are most satisfactorily seen in ad- 



