392 



Comparative Animal Physiology 



Other arthropods have various arrangements of ocelH. Many species have 

 ocelH with several retinulae; others (myriopods) have groups of such ocelH 

 placed contiguously so that they may tend to simulate a compound eye; 

 Limulus has' a numher of ocelli, each with a single retinula, closely spaced 

 to form the lateral eyes, which are somewhat similar in function to the true 

 compound eye; and Crustacea have true compound eyes similar to those of 



insects. 



The Photic Behavior of Arthropods. The presence of a compound eye, 

 consisting of many ommatidia, supplemented by additional ocelli, provides 

 an organism wit} a great number of individual photoreceptors pointing in 

 different directions. 



Fig. 106. Diagram to show image formation, by (A) an apposition eye and (B) a 

 superposition eye. a-f. Luminous points with the rays emitted by them; P, pigment; Rh, 

 rhabdom. After Kiihn, from Wigglesworth."^ 



Lens 



Matrix cells of lens 



Rhabdom 

 Pigment 



Nuclei of retinula cells 

 Nerve 



Fig. 107. Ocellus of Aphrophora spumaria (after Imms and Link). From Wigglesworth.^'^ 



