CH. XV.] DIPTEROUS INSECTS. 213 



been granted to our insects ; for Reaumur remarked, 

 that the eggs were deposited on all substances in- 

 discriminately. Hurried as the operation is in such 

 creatures, one would naturally suppose that they 

 who had so much to do in their short life, surrounded 

 with the same dangers as if the natural term of ex- 

 istence were longer, would not be required to do 

 more in that short period than the rest of their 

 tribe, but would be exempted from ordinary labours ; 

 but nature has crowded into their short life an oper- 

 ation to which other insects are not subjected. 

 After they have gone through the ordinary meta- 

 morphoses common to most insects, and when 

 they are apparently perfect insects, they again cast 

 their skins and change a vestment which has 

 scarcely time to become old. 



CHAPTER XV. 



THE NATURAL HISTORY OF VARIOUS OBNOXIOUS SPECIES OP 

 DIPTEROUS INSECTS. 



Distribution of Species and Individuals Housefly Structure of 

 its mouth Power of walking against Gravity Ovoviviparous 

 Flies The Blowfly and Blue-BottleflyWheatflyHessianfly 

 German Wheatfly Choral Dances of Summer and Winter 

 Midges Midnight Gyrations of Midges Gnat. 



ONE of the most interesting questions connected 

 with zoological science, is that which has reference 

 not only to the numerical distribution of the spe- 

 cies of animals, but to that of individual specimens of 

 any given species. In a state of nature, it is per- 

 haps undoubted, that the larger the animal the fewer 

 will be the individuals of which its species is com- 

 posed; although it cannot be questioned that the 

 quantity of each is limited by a far higher consid- 

 eration, namely, that of apportioning the number 



