Parker. — Compound Eyes in Crustaceans. 



PLATE VI. 



Serolis. 



Figures 60 to 64 inclusive represent the structure of the ommatidium in the 

 adult. Figures 65 to 72 are drawn from sections of ommatidia in well ad- 

 vanced embryos. All figures are magnified 475 diameters. 



Fig. 60. A tangential section through the most distal portion of the retina. This 

 section includes a portion of a cone and the tissue lying between it 

 and two adjoining cones. 



" 61. A transverse section ofaretinula in the region of its rhabdome. The 

 arrangement of the pigment granules and nerve fibrillae is indicated 

 in only one of the four cells. Of the two lines which appear to 

 separate the cone cell6 (cl. con.) from the rhabdomere (rhb'm.), the 

 one nearer the axis of the ommatidium is the real line of separa- 

 tion ; the other lies within the substance of the rhabdomere itself 

 (compare p. 92). 



" 62. A transverse section through a retinula proximal to the rhabdome and 

 in, the region of the hyaline cell. As in Figure 61, the pigment 

 granules are drawn in only one of the retinular cells. 



" 63. A transverse section through a single retinular cell in the region of its 

 nucleus. The axis of nerve fibrillae is represented by several small 

 axes in the substance of the cell at one side of the nucleus. 



" 64. A transverse section of the fibrous ends of the cells of one retinula in 

 their passage through the aperture in the basement membrane. 

 Each cell shows a well marked fibrillar axis, the centre of which is 

 often occupied by a core of pigment. The basement membrane is 

 viewed from its distal face. The irregularly oval body in the upper 

 left-hand corner of the figure is probably a nucleus. It lies on the 

 proximal face of the membrane through which it is seen. 



" 65. A longitudinal section through the ommatidium of an advanced embryo. 

 The numbers at the left of the figure correspond to the numbers of 

 the six following figures of transverse sections, and indicate the 

 levels at which the latter were taken. Figure 68 represents a sec- 

 tion so nearly in the same plane as that shown in Figure 67 that its 

 number has been omitted. 



" 66. A transverse section at the level of the corneal hypodermis. 



" 67. A transverse section through the distal end of a cone. 



" 68. A transverse section made in a plane only slightly proximal to that 

 shown in Figure 67. 



" 69. A transverse section through the region of the distal retinular nuclei. 



" 70. A transverse section through the proximal ends of the cones. 



" 71. A transverse section through the retinula in the region of the rhabdome. 



" 72. A transverse section at the level of the proximal retinular nuclei. 



