104 BULLETIN OF THE 



to me to involve that of the origin of the similar cells beneath the 

 retina. If I ain right in this conclusion, all these cells must either have 

 arisen in the retina, many of them migrating in a proximal direction 

 out of it, or they must have had some extra-retinal origin, some of them 

 migrating into it. On account of the considerable numbers in which they 

 exist in the spaces below the retina, it seems to me much more probable 

 that they have had an extra-retinal origin than that they have come 

 from the retina itself. If this is their source, it is evident that those 

 which are in the retina are intrusive. The nucleus which has already 

 been mentioned as caught in an opening of the basement membrane 

 (Fig. 91) has more the appearance of a body which is making its way 

 into the retina than of one which is moving in the reverse direction, 

 and may therefore be regarded as confirming to some extent the view 

 of the extra-retinal origin of these cells. Their source, however, cannot 

 be stated with certainty. Their power of migration implies amoeboid 

 activity, and this might be taken as an indication of their mesodermic 

 origin. 



The following cells characterize the ommatidium of Mysis : cells of 

 the corneal hypodermis, two : cone cells, two ; j)roximal retinular cells, 

 eight, one of which is rudimentary ; distal retinular cells, two ; accessory 

 pigment cells (mesodermic 1) present. 



Stomatopoda. 



The material which I have had for the study of the eyes in the Stoma- 

 topods consisted of two specimens of Gonodactylus chirarga, Latr. These 

 were kindly given me by Mr. W. S. Wadsworth, who had collected them 

 in the Bermudas. One of them had been killed in hot water and pre- 

 served in alcohol ; the other was both killed and preserved in strong 

 alcohol ; both were in excellent histological condition. 



In Gonodactylus, as I have previously mentioned, there are two kinds 

 of ommatidia ; these differ in no important respect except size. 



Longitudinal sections of both kinds are represented on Plate VIII. ; 

 the figure of the larger kind (Fig. 94) is taken from a depigmented sec- 

 tion, that of the smaller one (Fig. 95) from a section containing the 

 pigment in its natural condition. In the following description I shall 

 give an account of the structure of the larger ommatidia, alluding to 

 the condition of the smaller ones only when it differs in some important 

 respect from that of the others. 



The corneal hypoderviis is represented in the ommatidium of Go- 

 nodactylus by two cells, the nuclei (Figs. 94-96, nl. cm.) of which can 



