Parker. — Compound Eyes in Crustaceans. 



PLATE V. 



P or cell to. 



Fig. 46. 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 robusla, Kroyer. 



(Figs. 47, 48.) 



Fig. 47. A transverse section through the distal end of a retinula. The bodies, 

 one of which is marked x, 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. 

 " 48. A transverse section through three ommatidia in the region of their 

 rhabdomes. X 475. 



Idotea irrorata, M. Edws. 



(Figs. 49-57.) 



Fig. 49. 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. X 140. 



" 50. 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. 



" 51. A transverse section through the distal ends of the cones. X 475. 



" 52. A transverse section through the middle region of a cone. X 475. 



" 53. A transverse section through the middle of a retinula. Near the centre 

 of each cell can be seen a small axis of nerve fibrillae. X 475. 



" 54. 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. 



" 55. 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 53. X 475. 



" 56. A transverse section of several groups of retinular cells immediately 

 proximal to the basement membrane. X 475. 



" 57. A transverse section of four retinular cells at the level in which their 

 nuclei occur. The axis of nerve fibrillae 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). 



Sphceroma. 



(Figs. 58, 59.) 



Fig. 58. A transverse section of a retinula at a level slightly distal to the base 

 ment membrane. X 475. 

 " 59. 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 fibrillae is the 

 more transparent condition of the central part of the cells, due to the 

 partial absence of pigment granules. X 475. 



