Parker. — Compound Eyes in Crustaceans. 



PLATE IX. 



Palcemonetes. 



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



Fig. 103. A longitudinal section of an ommatidium. The numbers at the left of 

 the figure correspond to the numbers of nine of the following fig- 

 ures of transverse sections, and mark the levels at which the latter 

 were taken. 



''" 104. A longitudinal section of an ommatidium which has been depigmented. 

 The bodies marked x resulted from the action of the depigmenting 

 reagent. 



" 105. A facet from the corneal cuticula ; cleaned in strong potassic hydrate, 

 and examined from its distal side in water. 



" 106. A transverse section through the region of the corneal hypodermis. 



" 107. A transverse section through the distal end of a cone in the region of 

 the nuclei of the cone cells. 



" 108. A transverse section through the middle of a cone. 



" 109. A transverse section through parts of four ornmatidia in the region of 

 the distal retinular nuclei. 



Figures 110-112 represent three successive transverse sections, each through 

 five ornmatidia, in the region of their proximal retinular nuclei. Only the 

 outlines of the nuclei and the five groups of cone cells (cl. con.) are drawn. 

 The nuclei in each ommatidium are numbered from 1 to 7, and as their plan 

 of arrangement is the same in the different ornmatidia, corresponding nuclei 

 have been designated by the same number. In some cases the nuclei were 

 cut in two, and consequently appear in two adjoining sections. In such 

 cases the two parts have been marked with the same number. Figure 110 

 is the most distal of the series; Figure 112, the most proximal. 



Fig. 113. A transverse section of the retinula near the distal end of the rhabdome. 



Depigmented. 

 " 114. A transverse section of four retinulae at the level of the eighth retinular 



nucleus. 

 " 115. A transverse section through four retinulae in the region of the accessory 



pigment cells; viewed by reflected light. The retinula? appear as 



dark masses embedded in a whitish field composed for the most part 



of the substance of the accessory pigment cells. 

 " 116. A transverse section through a retinula at about the same level as that 



shown in Figure 115. Depigmented. 

 " 117. A transverse section through the optic nerve fibres at a level slightly 



proximal to the basement membrane. Depigmented. 



