ON GENERATION. 291 



embryos. And here that practice of the poor folks finds its 

 application : " Having hens at home, but no cock, they commit 

 their females to a neighbour's male for a day or two ; and from 

 this short sojourn the fecundity of the whole of the eggs that 

 will be laid during the current season is secured." 1 Not only 

 are those eggs which are still nothing more than yelk and have 

 no albumen, or which exist only as most minute specks in the 

 ovary, but eggs not yet extant, that will be conceived long after- 

 wards, rendered fertile by the same property. 



EXERCISE THE THIRTIETH. 



Of the uses of this disquisition on fecundity. 



This disquisition on the inherent qualities of the egg and the 

 cause of its fecundity, is alike in point of difficulty and subtlety, 

 but of the highest importance. For it was imperative on us to 

 inquire what there was in the conception, what in the semen 

 masculinum, and what in the female fowl, which render these 

 fertile ; and what there is in the fruitful cock which makes him 

 diifer from a bird that is barren. Is the cause identical with that 

 which we have called the vital principle (anima) in the embryo, or 

 it is a certain portion of the vegetative principle ? Because, 

 in order to apprehend the entire cause of generation, it is of 

 much moment that the first cause be understood ; for science is 

 based upon causes, especially first causes, known. Nor is this 

 inquiry less important in enabling us to understand the nature 

 of the vital principle (anima). These questions, indeed, rightly 

 apprehended, not only are Aristotle's opinions of the causes of 

 generation refuted or corrected, but all that has been written 

 against him is easily understood. 



We ask, therefore, whether it is the same thing or something 

 different, which in the rudimentary ovum, yelk, egg, cock and 

 hen, or her uterus, confers fruitfulness ? In like manner in what 

 respect does this something agree or differ in each ? Still far- 

 ther, is it a substance whence the fecundating virtue flows? 



1 Fabricius, op. cit. p. 37. 



