Parker. — Com])ound Eyes iii Crustaceans. 



PLATE V. 



Porctllio. 



Fig. 46. A transverse section through a retinula in a plane slightly distal to the 

 basement membrane. The single, light, central spot represents the 

 pro.ximal end of tlie rhabdome. X 475. • 



hlutca robusta, Kroyer. 



(Figs. 47, 48.) 



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



one of which is marked .r, are splieres of coagulated material wliicli 



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 fibriliae. 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). 



Sph(eroma. 

 (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 fibrillaj is the 

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

 partial absence of pigment granules. X 475. 



