100 BULLETIN OF THE 
hypodermis, and two to the cone cells, correspond without much doubt’ 
to the so called four Semper’s nuclei mentioned by Claparéde (’60, 
p. 194) in Mysis flexuosa, and described by Sars (’67, p. 33) in M. ocu- 
lata. Nusbaum (’87, p. 179) also observed four similar nuclei in the 
developing eye of Mysis chameleo, and Grenacher (’79, p. 118) described. ” 
the same number in Mysis vulgaris. In the last named species, accord- 
ing to Grenacher, 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 
to 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, 
Grenacher (’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, cta.). In this respect, therefore, different species probably vary. 
The cones in Mysis vulgaris, according to Grenacher (’79, p. 118), are 
composed of two segments. The same number is also present in the 
cones of M. stenolepis (compare Figs. 76-78, 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. 
