138 INSECT MISCELLANIES. 



iris (Z)j or at least a uvea, which allows the light to 

 pass only through the centre of the apparatus. 

 There is also a perforation, a true pupil, which appears 

 black, as in man, when examined with a powerful 

 magnifier. The whole of these pupils, whose axes 

 correspond to that of the eye of the observer, form 

 the black and mobile spot which has often been a 

 source of embarrassment to those examining these 

 parts. 



" In the Lucanus Cervus, the cornea (a) is of ex- 

 traordinary thickness, and its facets are accordingly 

 so much elongated as to appear like prisms. The 

 cones have their bases nearly in contact with the 

 cornea, and at that part are apparently without pig- 

 ment; towards their apices, where they are attached 

 to the nervous filaments, they are surrounded with 

 pigment of a violet colour. The nervous filaments, 

 also, in the greater part of their course from the 

 optic nerve, are without any investiture of coloured 

 matter." 



Numerous details of a similar minute kind are given 

 of the eyes of many other insects, but what we have 

 now quoted will show the nature of these researches. 

 We cannot, however, omit one other extract, exhi- 

 biting M. Miiller's idea of the principles of insect 

 vision. " The following figure," we again use the 

 words of Mr. Parsons, " represents the section of a 

 compound eye, in order to show the course of 



