252 



TEXT-BOOK OF ENTOMOLOGY 



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

 Hymenoptera (Fig. 20.'!). 



FIG. 263. Two sepa- 

 rate elements of the eucone 



FIG. 262. Ommatidium eye of a bee ; Lf, cornea ; 

 of cockroach (Periplaneta) : n, nucleus of Semper ; Kk, 

 If, cornea ; kk, crystalline crystalline cone ; Py , pig- 

 cone ; pff', pigment cell; rl, ment cells; Kl, retinula; 

 retinula ; rm, rhabdom. Af- Rm, rhabdom. After 

 ter Grenacher, from Lubbock. Grenacher, from Lubbock. 



a. Pseudocone eyes ; in which, instead 

 of the crystalline lens or cone, there 

 are four, cells rilled 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 

 pseudocone 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 four primitive cone-cells. 

 Acone eyes occur in Forfieulidse, 

 Hemiptera (except Cicadidae), the ne- 

 matocerous Diptera (Tipula, etc.), and 

 those Coleoptera which have less than 

 five tarsal joints. 



n 



bm 



Vm. 



- Va. 



FIG. 264. Three ommatidia of a 

 pseudocone eye. diagrammatic : A, a 

 separate ommatidimn of .!/'/*<,; r<ni- 

 ttii'/d. semi-diagrammatic: c, cornea; 

 p.c, pseudocone; pij'. piinnonted cells 

 surrounding the pseiiilocnnt- : /'.,'/.j, :nl- 

 ditional pigment ccll^ ; /'.;/ :i . bMM ]>itr- 

 ment cells; n.p.c, nuclei of paeadooone : 

 r, retinula-; ./. /'./ .nucleus of retinu- 

 b : /,'. rhabdom ; b.m, basal membrane; 

 t.n . terminal anastomosis sending ni-rvi- 

 fibrilsto tht-rctiiiuhi-. B. section through 

 a retinula and rhabdom near the basal 

 nii-nibrani'. the six ivtintila- (/ t'n^nl 

 into a tube ensheathing the rhabdom 

 (ft). A ft. -r Hickson. 



