62 INTRODUCTION. 



terruptcdly possessed since the first establishment of species. 

 The oldest records of natural history, where sullieiently 

 clear to be relied upon, show us that in the species which are 

 therein described or figured, not the least variation has taken 

 place in them. Were not this the case, indeed, there would 

 be grounds for the belief that there are new species of ani- 

 mals produced, which, as Ray says, would certainly now and 

 then, nay very often, happen were there any such thing. 

 But, as in the higher animals, the species of insects are liable 

 to variation, as every collector is well aware ; thus, some 

 moths, which have the ground of their wings of a pale 

 colour with dark markings, will be found to have dark wings 

 with light marks. Variations in size are equally common, 

 and entomologists deem it expedient to retain in their col- 

 lections suites of individuals of each variable species, from 

 the smallest to the largest : sometimes, indeed, the latter are 

 many times larger than the former, a circumstance often 

 occurring in wood-feeding insects. In general, also, male 

 insects are much smaller than the females. The reader will 

 also bear in mind that this variation in size is not the result 

 of increased growth after arrival at the winged state, and that 

 the small individuals will by and bye attain the size of their 

 partners. This is quite contrary to every principle of in- 

 sect physiology. It is in the larva state that the eating 

 and growing of these animals chiefly takes place. And it 

 woidd be as requisite for the imago to cast its horny en- 

 velope, in order to increase its size, as it is for the 

 larva to do the same thing : again, it must be self-evident 

 that without the sloughing, the external envelope could 

 never, from its consistence, undergo the slightest change 

 after once attaining maturity. Moreover, the change which 

 the digestive organs undergo in the passage from the larva 

 to the imago states, sufficiently proves the same fact. Hut 

 species often vary even in structure, not indeed in any of the 



