PARKER. — Compound Eyes in Crustaceans. 
Fig. 46. 
Fig. 47. 
see io} 
Fig. 49 
* 60. 
Thy aks 
uae i) 
Sheri) 
“64. 
AD: 
ray) see 
pay A 
Fig. 58 
Sa e0p. 
PLATE V. 
Porcellio. 
A transverse section through a retinula in a plane slightly distal to the 
basement membrane. The single, light, central spot represents the 
proximal end of the rhabdome. X 475. 
Idotea robusta, Kroyer. 
(Figs. 47, 48.) 
A transverse section through the distal end of a retinula. The bodies, 
one of which is marked wz, are spheres of coagulated material which 
occur in the interommatidial spaces, and which have been brought 
into prominence by the action of the hardening reagent. X 475. 
A transverse section through three ommatidia in the region of their 
rhabdomes.  X 475. 
Idotea wrrorata, M. Edws. 
(Figs. 49-57.) 
The anterior face of a section transverse to the chief axis of the body, 
and passing through the eye on the right side of the head. Xx 140. 
A longitudinal section of an ommatidium. The numbers at the left of 
the figure correspond to the numbers of the following six figures 
of transverse sections and mark the levels at which the latter were 
taken. X 475. 
A transverse section through the distal ends of the cones. 475. 
A transverse section through the middle region of a cone.  X 475. 
A transverse section through the middle of a retinula. Near the centre 
of each cell can be seen a small axis of nerve fibrilla. > 475. 
A transverse section through a retinula composed of seven cells instead 
of six. This section was cut approximately at the same level as that 
shown in the preceding figure. X 475. 
A transverse section through a retinula near its proximal end. Each 
fibrillar axis is much larger at this plane than in that shown in Fig- 
ure 58. xX 475. 
A transverse section of several groups of retinular cells immediately 
proximal to the basement membrane.  X 475. 
A transverse section of four retinular cells at the level in which their 
nuclei occur. The axis of nerve fibrille in the plane of this section 
and in that of the preceding one (Fig. 56) are smaller than they 
are at the base of the retina (compare Fig. 55). 
Spheroma. 
(Figs. 58, 59.) 
A transverse section ofa retinula at a level slightly distal to the base 
ment membrane. X 475. 
A transverse section of the fibrous ends of the cells from a single re- 
tinula. The plane of section is slightly proximal to the basement 
membrane. ‘The only indication of an axis of nerve fibrille is the 
more transparent condition of the central part of the cells, due to the 
partial absence of pigment granules.  X 475. 
