254 Microscopical Essays. 



are fome years in a manner freed from them. The fame kind of 

 animal is then at one time of the year viviparous, and at another 

 ©viparous. 



Thofe aphides which withftand the feverity of the weather fel- 

 dom come to their full growth before the month of April, at 

 which time they ufually begin to breed, after twice calling off 

 their exuvia, or outward covering. It appears that they are all 

 females, which produce each of them a numerous progeny, and 

 that without having intercourfe with any male infeft ; they are 

 viviparous, and what is equally lingular, the young ones all come 

 into the world backwards. When they firft come from the 

 parent, they are enveloped by a thin membrane, having in this 

 fituation the appearance of an oval egg; thefe egg-like appear- 

 ances adhere by one extremiry to the mother, while the young 

 ones contained in them extend the other, by that means gradually 

 drawing the ruptured membrane over the head and body to the 

 hind feet. During this operation, and for fome time after, the 

 fore part of the head adheres, by means of fomething glutinous, to 

 the vent of the parent. Being thus fufpended in the air, it foon 

 frees itfelf from the membrane in which it was confined ; and 

 after it's limbs are a little ftrengthened, is fet down on fome 

 tender moots, and left to provide for itfelf. 



In the fpring months there appear on the rofe trees but two 

 generations of aphides, including thofe which proceed immedi- 

 ately from the laft year's eggs • the warmth of the fu miner adds 

 fo much to their fertility, that no lefs than five generations 

 fucceed one another in the interval. One is produced in May, 

 which calls off it's covering; while the months of June and July 



each 



