222 NATURAL HISTORY. [CH. XV. 



blowfly (Musca carnaria) belongs to the modem sub- 

 genus Sarcophaga, so named in allusion to its feed- 

 ing upon flesh, carrion, &c. This insect, and sev- 

 eral of its congeners, instead of laying eggs, as do 

 the majority of insects, deposite their young in the 

 state of larvae or footless grubs, the eggs being pre- 

 viously hatched within the body of the parent. 

 These insects have been termed viviparous by 

 some authors; this term has, however, been ob- 

 jected to, in consequence of the embryos of none 

 of these insects being nourished, as in the true 

 viviparous animals, within a uterus, by means of a 

 placenta, but developed within true eggs, which are 

 hatched within the body of the mother, as was 

 proved by De Geer, who discovered real eggs within 

 the body, as well as newly-hatched larvae ; whence 

 the term ovo-viviparous, a term applied to the sim- 

 ilar mode of production which occurs in the vipers 

 and other reptiles, — has been suggested by Messrs. 

 Kirby and Spence, to designate this species of par- 

 turition. 



Perhaps there could not be adduced a more stri- 

 king instance of that " harmony of nature," of which 

 we have before spoken, than is afforded by the flies 

 at present under consideration; their function is 

 to consume and cleanse the surface of the earth 

 from dead and putrefying animal matter. Now, for 

 this purpose it is requisite, not only that no time 

 should be lost in the development of the agents em- 

 ployed in this task, but also that their numbers 

 should be increased in proportion to the extent of 

 their duty. Here, therefore, we find both these 

 objects attained in the fullest manner, but by extra- 

 ordinary means : the eggs of the fly being hatched 

 within its own body, no time is lost when they are 

 deposited upon a carcass, neither is there any 

 danger of their being destroyed by being placed in 

 the midst of the putrefying mass, which might have 

 been the case had eggs been there deposited. Fur- 



