252 



TEXT-BOOK OF ENTOMOLOGY 



joints, in the dipterous genus Corethra, and in the Lepidoptera and 

 Hymenoptera (Fig. 263). 



kfr 



13' 



rm 



FIR. 262. Ommatidium 

 of cockroach (Periplaneta) : 

 If, cornea ; kk, crystalline 

 cone ; pg', pigment cell ; rl, 

 retinula ; rm, rhabdom. Af- 

 ter Grenacher, from Lubbock. 



Urn. 



Fifi. 263. Two sepa- 

 rate elements of the eucone 

 eye of a bee ; Lf, cornea ; 

 n, nucleus of Semper ; Kk; 

 crystalline cone ; Pg , pig- 

 ment cells; Rl, retinula; 

 Rm, rhabdom. After 

 Grenacher, from Lubbock. 



a. Pseudocone eyes ; in which, instead 

 of the crystalline lens or cone, there 

 are four cells filled with a transparent 

 fluid medium, and a smaller protoplasmic 

 portion containing a nucleus (Muscidae, 

 Fig. 264, pc). Hickson states that the 

 difference between the eucone and pseu- 

 docone eyes lies in the fact that in the 

 pseud ocone eye "the refracting body 

 formed by the cone-cell lies behind the 

 nuclei," and in the eucone eye in front 

 of it. 



2. Acone eyes, where the cone or re- 

 fracting body is wanting, but is repre- 

 sented by the foui- primitive cone-cells. 

 Acone eyes occur in Forficulidae, 

 Hemiptera (except Cicadidse), the ne- 

 rnatocerous Diptera (Tipula, etc.), and 

 those Coleoptera which have less than 

 five tarsal joints. 



B 



Vnv 



--la. 



Fir,. 264. Three ommatidia of a 

 pseudocone eye, diagrammatic: .1. a 

 separate onimatidium of MHKCH romi- 

 tu/'iit, semi-diagrammatic: o, cornea; 



/<.( pseudocone ; i>(i' , piirmented ('"'Us 

 suiToundinir the psendoeone ; J>.(/ 2 . ad- 

 ditional pisrinent cells; !>.(!$, basal pip- 

 inent cells ; n.p.c, nuclei of pseudocone ; 

 /, retinulte; >!./', .>', nucleus of retinu- 

 l;e ; /.', rhabdom : /'.///, basal inembrane; 

 f.it, terminal anastomosis sendiiifr nerve- 

 fibrils to theretinula'. B, section through 

 a retinula and rhabdom near the basal 

 membrane, the six retinulte (r) fused 

 into a tube ensheathing the rhabdom 

 (ft). After Hickson. 



