UNIFORM SIZE OF INSECTS. 347 



of the same species, differing in nothing, except, 

 perhaps, in the size; the latter being erroneously 

 ascribed to difference of age. But the fact is, that 

 there are a considerable number of species of our 

 white butterflies, as well as several genera, and pro- 

 bably more varieties even of these than have yet been 

 ascertained or described. It is certain, indeed, that 

 butterflies do not, like the larger animals, increase 

 in size as they grow^ older; for every individual, 

 from the moment it becomes a butterfly, continues 

 invariably of the same size till its death. Butter- 

 flies, indeed, seldom live longer than a few days, or 

 at most a few weeks, and during this time they eat 

 little, except a sip of honey: and since this is so, it 

 would be absurd to expect that they could increase in 

 size. ' It must not, however, be understood from this, 

 that the same species will always measure or weigh 

 precisely the same; for though this will hold as a 

 general rule, there are many exceptions, arising from 

 the accidents the caterpillar may have suffered from 

 which an individual butterfly originated. It is only 

 during the caterpillar state that the insect eats vora- 

 ciously, and grows in proportion; and if it is, during 

 this stage of its existence, thrown upon short allow- 

 ance, it cannot acquire the standard magnitude, and 

 the butterfly will be dwarfed from the first. The 

 same remarks with respect to growth apply to insects 

 of every kind, and the fact cannot be better exemplified 

 than in the uniformity of size in the house fly (Musca 

 domeslica) among which scarcely one individual in a 

 thousand will be found to differ a hair's breadth in 

 dimensions from its fellows.'* 



We may add, that there are many flies occasion- 

 ally found in houses both larger and smaller than the 

 Musca domestica, but these are of a different spe- 



* J. Rennie on the White Butterflies of Britain, Mag. Nat. 

 Hist, vol. ii, p. 225. 



