GENERATION OF ANIMALS. 259 



May not this retention of fuperfluous nourlfh- 

 ment, which cannot efcape by tranfpiration, be 

 one reafon of the extraordinary fertility of thefe 

 animals, and of their being able to fubfift a long 

 time without food ? All birds and flying infedts 

 are oviparous, except fome fpecies of flies which 

 produce their young alive *. Thefe have no 

 wings immediately after their birth ; but they 

 gradually fhoot out as the animal advances in 

 growth ; and they are not in a condition to be 

 ufed till it acquires full maturity. All fhell- 

 fiflies are oviparous; and llkewife rhofe reptiles 

 that have no feet, as fnakes and ferpents ; they 

 change their fkins, which are compoied of fmali 

 fcales. The viper is but a flight objection to 

 this general rule ; for it is not properly vivipa- 

 rous. It firft produces eggs, from which the 

 young are hatched : This operation is indeed 

 carried on and completed in the body of the 

 mother; and, infl;ead of laying the eggs, like 

 other oviparous animals, the viper hatches them 

 within the body. The lalamander, in which, as 

 Maupertuis remarks t, both eggs and young are 

 found at the fame time, is a fnnilar exception in 

 oviparous quadrupeds. 



Mofl: animals are multiplied arid perpetuated 

 by copulation. But many animals, as the great- 

 ell number of birds, propagate rather by a kind 

 of compreflion, than a proper copulation. Some 



R 2 birdsj 



* See Leeuwenhoek, torn. 4. p. 91. 

 f Mem. de I'Acad. ann6e 1727, p. 32. 



