100 BULLETIN OF THE 



hypodermis, and two to the cone cells, correspond without much doubt 

 to the so called four Seiuper's nuclei mentioned by Claparede ('CO, 

 p. 194) in Mysis flexuosa, and described by Sars ('07, p. 33) in M. ocu- 

 lata. Nusbaum ('87, p. 179) also observed four similar nuclei in the 

 developing eye of Mysis chameleo, and Grenadier ('79, p. 118) described 

 the same number in Mysis vulgaris. In the last named species, accord- 

 ing to Grenadier, the four nuclei are grouped in two pairs, one of which 

 occupies a more distal plane in the ommatidium than the other. The 

 more superficial pair undoubtedly belongs to the corneal hypodermis, the 

 deeper pair to the cone cells. 



It must be evident, then, that the nuclei of the cone cells and corneal 

 hypodermis have not always been carefully distinguished. In all cases 

 where they have been separated, the corneal hypodermis has been shown 

 tb possess two nuclei for each ommatidium. 



The corneal cuticula in Mysis, as Frey and Leuckart ('47*, p. 113) 

 first pointed out, is facetted, and the outline of the facet is a circle. 

 In Mysis stenolepis the circumference of the facet is tangential to the 

 circumferences of six adjoining facets (Fig. 74). In Mysis vulgaris, 

 Grenadier ('79, p. 118) has shown that the facet is not lens-like, but is of 

 uniform thickness throughout. In M. stenolepis. however, the cuticula 

 is often slightly thicker at the middle of the facet than at its edges (Fig. 

 73, eta.). In this respect, therefore, different species probably vary. 



The cones in Mysis vulgaris, according to Grenadier ('79, p. 118), are 

 composed of two segments. The same number is also present in the 

 cones of M. stenolepis (compare Figs. 7G-78, con.). In longitudinal sec- 

 tions the cone (Fig. 73, con.) appears to consist of a uniformly and finely 

 granular substance enveloped in a delicate but distinct membrane. 

 Near the distal end of the cone the material which composes it becomes 

 more coarsely granular ; in this the nucleus of the cone cell is usually 

 lodged. Cones (Fig. 92) which have been isolated in macerating fluids 

 are plumper and apparently not so contracted as those which have been 

 subjected to the process of cutting. The nuclei also are rounder and fuller. 

 The cone proper (Fig. 92 con.) occupies a more central position in the 

 cone cells, and is surrounded by a finely granular material, which is es- 

 pecially abundant at the proximal end. The difference between the cone 

 proper and this granular material was not generally observable in sections 

 of the cones. In all of the many cones which I succeeded in isolating, 

 the proximal ends invariably had a broken appearance. Consequently, I 

 believe that I have never completely isolated a pair of cone cells. The 

 question of the proximal extent of the cone I shall recur to later. 



