Parker, — Compound Eyes in Crustaceans. 



PLATE X. 

 In all Figures on this plate tiie magnification is 475 diameters. 



Camburus. 

 Figures 118-122 represent a series of five successive transverse sections tlirougli one 

 and parts of four adjoining ommatidia in tlie region of tlieir proximal 

 retinular nuclei. Figure 118 represents the most distal section m 

 the series, Figure 12'2, the most proximal. In these figures, only 

 the outlines of the nuclei and the groups of cone cells are drawn. 



Crangon. 



Fig. 123. A transverse section through a number of ommatidia in the region of 

 their distal retinular nuclei. 



PaJmurus. 



Fig. 124. A transverse section through a retinula in its middle region. The out- 

 lines of the retinular cells cannot be distinguished ; the position of 

 each cell is marked by an irregular liglit mass in its centre. 

 " 125. A transverse section through a retinula in the plane of its eighth 

 nucleus. Depigmented. 



Cancer. 



(Figs. 126-131.) 



Fig. 126. A corneal facet viewed from its distal surface. The cuticula from which 

 this facet was drawn was cleaned by being boiled in a strong aqueous 

 solution of potassic hydrate. It was examined in water 



" 127. A transverse section of the distal end of a cone. 



" 128. A transverse section through three ommatidia at the level of the distal 

 retinular nuclei. The pigment granules have been indicated m only 

 the lower circle of cells. 



" 129. A transverse section through the distal region of four retinular. In the 

 two on the right, the pigment granules have not been drawn 



" 130. A transverse section througli a retinula near the base of the retina. 



" 131. A slightly oblique section through the basement membrane. The upper 

 part of the figure represents the retinulae as seen m transverse sec- 

 tion distal to the basement membrane; the part marked mb. ba. 

 represents the region in which the membrane itself appears ni section, 

 and the lower half of the figure sliows the cut fibres of the optic 

 nerve. The pigment granules are omitted from the right side of the 

 figure. The transition from the retinular cells to tiie nerve fibres 

 is evident in passing over the section from top to bottom. 



