292 



ANIMAL PHYSIOLOGY. 



[LESSON 91. 



FIG. 413. 



FIG. 414. 



Transparent cornea, with 



lenses in situ; M. 



carnaria. 



Lamina of the transparent 

 cornea, containing the len- 

 ses, Caterpillar. 



taining the lenses in situ. In some Insects this membrane is partic- 

 ularly delicate, and in these cases it is more likely to remain attached 

 to the transparant cornea, showing the lenses, when viewed by trans- 

 mitted light, in the centre of the facets, severally; this is shown 

 from a preparation of the Flesh-fly (Musca carnaria), Fig. 413. A 

 beautiful specimen of the membrane, detached, with the lenses, was 

 obtained from a small Caterpillar of this country, name unknown ; 



a figure of it is given 

 (Fig. 414). In this 

 specimen the lenses are 

 of unusual size, the pos- 

 terior surface being of 

 great convexity. 



1318. The conical 

 bodies are usually col- 

 ored, but very delicate 

 in texture, and possessing a semi-transparency. 



1319. They have generally a faint yellow color, and they become 

 decomposed in a very short time in water ; neither can they be pre- 

 served very well any how ; in spirit they contract so much as not to 

 be visible, and in other preserving fluids it is extremely difficult for 



the well-practised eye to detect them ; 

 hence they should be sought for in 

 freshly caught insects. 



1320. All authors agree in believ- 

 ing the conical lenses to represent the 

 vitreous humor of the eyes of the 

 higher animals, a fact confirmed by 

 the difliculty of preserving them. 



1321. They are undoubtedly con- 

 vex at their large extremity, and in 

 some insects (M. carnaria) remarka- 

 bly so. 



1322. The optic filaments are not 

 attached to the terminal points or api- 

 ces of the cones as represented by au- 

 thors, but, on the contrary, pass en- 

 Conical bodies, Cone of a cater- tirel y through their centre (b, Fig. 



M carnaria. pillar. 415) an( j are some times Seen pro- 



a. Cone. /' * 



6. Optic filament. jecting through the large end (base 



of the cone). In Musca carnaria, examined by a fourth object-glass, 



FIG. 415. 



FIG. 416. 



