THE 



PART I 



below the connective tissue layer. In this way we 

 get the double layer of cells composing the typical 

 Crustacean eye. 



cc 



FIG. 23. Diagram of two single eyes cf the paired eyes of Apus. hy, original 

 undifferentiated hypodermis cells secreting outer cuticular membrane. cc, 

 crystal cone cells = differentiated hypodermis cells secreting the cones (<:>) ; cl, 

 layer of connective tissue fibres =subhypodermal connective tissue layer', r, 

 retinulae, i.e., groups of sensory (retinal) cells (re), with their rhabdoms (^//), 

 and pigment cells C/* 1 ) ; these belong to the hypodermis, but are thrust down 

 below the subhypodermal connective tissue layer by the cones. 



The great advantage of this separation of the cones 

 is not far to seek. The rounding off of the distal ends 



1 See Appendix II. on the pigment in these cells. 



