300 PTILOTA : INTERNAL ANATOMY. 



of which sighty hearing, smell, taste, and touch, are those 

 which are generally allowed to prevail. Some physiologists 

 (Dr. Virey, &c.) add to these, love, and the internal sense of 

 thought or instinct. The former of these, as a perception 

 distinct from the mere physical act of propagation, can 

 scarcely be allowed to insects. In this point of view the 

 subject cannot be discussed in a work like the present. The 

 instinctive powers of insects also appear to me to be on a 

 very different footing compared with the other senses. I 

 shall, therefore, defer my observations thereon to the subse- 

 quent section. 



That insects possess several of the senses is certain, but 

 the seat of these senses is not ascertained; neither can we, 

 by any possibility, arrive at a certain conclusion that the 

 senses of these animals are identical with our own, — their 

 entire organization having been shown to be so totally dif- 

 ferent from that of the vertebrated animals. Indeed, as Mr. 

 MacLeay has observed in the Horse Entomologies, there is 

 no reason why animals constituted upon a plan so totally 

 unhke our own should not possess senses of which we have 

 no idea. I will, however, adopt the general opinion, and 

 speak of the senses of insects as analogous to our own, the 

 consideration of which will form so many distinct sub-sec- 

 tions. 



(a) The Sense of Sight. — The eyes of insects are the only 

 organs which we can with any certainty refer to the sense of 

 which they are the seat. We have abeady described the ex- 

 ternal structure of the eyes, and ocelli or eyelets, and shall 

 therefore now notice their internal organization, and the 

 mode in which vision is effected. On making a perpendicular 

 incision into the eye, it is found to consist of various layers ; 

 the external membrane is hard, transparent, and composed 

 of a multitude of hexagonal facets, each forming a more or 



