The Subject I pitch upon, is that of the Formation of Animals, You know how wide and unsatisfying Men's Conjectures were upon this Head, until this Age, in which first the deservedly Famous Dr. _Harvey_ discovered the proper place of the Formation of the Chick in the _Cicatricula_ of the Egg, and the Formation of the Parts so far as was discernable by the naked Eye; and after him _Malpighius_, by the help of exact Glasses, observ'd the first Rudiments of it there, both before and after Incubation: And _R. de Graef_, and others, having upon many Observations concluded, that the _Testes Fœminei_ were the Ovaries of Females, and consequently that all Animals were _ex ovo_; they began from hence to infer, that the Rudiments of each Animal were originally in the respective Females, and that the Male contributed only to give a new Ferment to the Mass of the Blood and Spirits, by which means a spirituous Liquor (which the Blood in its ordinary Ferment could not produce) did insinuate it self into the same Ducts and Pores of the Rudiments of those Animals, which were in greatest forwardness in the Ovary, and so extend and enlarge all their Parts, and at last bring them to perfection, as Mr. _Perrault_ does ingeniously discourse in the third Part of his _Essais de Physique_; till now at last _Leowenhoek_ has discover'd an infinite number of _Animalcula in semine marium_ of all kinds, which has made him condemn the former Opinions about the Propagation of all Animals _ex Ovo_. Now upon comparing the Observations and Discoveries which have been made with one another, these three things seem to me very probable. 1. That Animals are _ex Animalculo_. 2. That these Animalcles are originally _in semine Marium_ & _non in Fœminis_. 3. That they can never come forward, nor be formed into Animals of the respective kind, without the _Ova in Fœminis_.