All quadrupeds covered with hair are viviparous; all those covered with scales oviparous. May we not then believe than in oviparous quadrupeds, a much less waste is made by transpiration, than the cloathing of scales retains; whereas in animals covered with hair this transpiration is more free and abundant? and is it not partly by this superabundance of nutriment, which cannot be carried off by transpiration, that those animals multiply so abundantly, and are enabled to go so long without food? All birds and all insects that fly are oviparous, excepting some kinds of flies which bring forth their young alive. These flies have no wings at their birth, but they shoot out and grow by degrees, and which they cannot use before they are of full growth. Scaly fish are likewise oviparous; as are all reptiles which have no legs, such as snakes and different kinds of serpents; they change their skins, which are composed of small scales. The viper is only a slight exception to the general rule, for it is not truly viviparous, as it produces eggs, from which the young are hatched; it is certain this is performed in the body of the mother, who instead of casting those eggs, like other oviparous animals, she retains and hatches them in her own body. The salamander, in which eggs and young ones are found at the same time, as observed by M. de Maupertuis, is an exception of the same kind in oviparous quadrupeds. Most animals are perpetuated by copulation; yet many birds seem only strongly to compress the females; indeed the ostrich, Crane, and some few others, are so well supplied as to leave intromission no ways equivocal. Male fish approach the female in the spawning time; they seem even to rub their bellies against each other, for the male often turns upon its back to meet the belly of the female; but the necessary part for copulation does not exist in them; and the male fish approaches the female only to emit the liquor in their milts on the eggs, which the female then deposits; and it seems rather to be attracted by the eggs than the female; for when she ceases throwing out the eggs, he instantly forsakes her, and with eagerness pursues the eggs, which the stream carries away, or that the wind disperses. Male fish may be seen to pass and repass every spot where eggs are deposited several times. It is certainly not for the love he bears the female that all these motions are made, because it is not to be presumed he always knows her; often being seen to emit his liquor on all eggs that he comes near, and that often before he has met with the female to which they belonged.