300 PTILOTA : INTERNAL ANATOMY. 



of which sight, 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 he 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 

 unlike 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 already 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 



