2 INTRODUCTION. 



are often very sharply separated from each other, involving an 

 entire change of form, although, in the case of insects with incom- 

 plete metamorphoses, the earlier stages pass gradually into the 

 later without involving so total a change as to resemble the pro- 

 duction of a new animal. In the larva state insects are sometimes 

 provided with from ten to twenty-two legs, but instead of this 

 number increasing, as in the Myriopoda, the number in the perfect 

 state, as already mentioned, is invariably six. In the perfect 

 state, too, insects, with rare exceptions in one or both sexes, always 

 acquire one or two pairs of wings, a character which does not 

 appear in any representative of the other three classes. 



Insects are frequently very highly gifted by Nature, much more 

 so, in fact, than the so-called higher animals. They are provided 

 with two large eyes, one on each side of the head, composed of 

 facets varying in number from sixteen to many thousands, accord- 

 ing to the species. In addition to these, many insects are provided 

 with one, two, or three visual organs, called simple eyes, ocelli, or 

 stemmata, placed in the crown of the head. Nor is this all, for the 

 compound eyes of certain water-beetles are actually divided hori- 

 zontally, so that, when swimming on the surface of the water, they 

 have literally two eyes to look upwards, and two to look down- 

 wards. Many observations have been placed on record, which 

 show plainly that insects can discriminate between colours, and 

 some recent experiments of Sir J. Lubbock on ants appear to 

 indicate that they are able to perceive the ultra-violet rays of the 

 solar spectrum, which are perfectly invisible to our eyes. 



Of the other senses of insects it is difficult to speak positively. 

 Their nervous system is composed of a double chain of ganglia, 

 and it is therefore probable that their perceptions are less exclu- 

 sively located in the brain than our own. Their hard integuments 

 protect them from liability to casual injuries from trifling causes, 

 and therefore we might be led to infer, a priori, that the sense of 

 pain would be of but little use to them. And this actually appears 

 to be the case, for they frequently appear to be just as lively and 

 comfortable after the severest injuries as before. It is scarcely 

 doubtful that they do not feel pain in anything like the same 

 degree as a vertebrate animal. 



But, with this exception, there is every reason to believe that 

 insects possess the same senses as vertebrate animals in the highest 

 perfection. Among the most important organs possessed by insects 

 are the antennae, two organs which project in front of the head, and 



