364 ON GENERATION. 



power, whence, subsequently, a fertile egg will be produced, 

 endowed with plastic powers, the consequence of a mixed na- 

 ture, or of a mixed efficient instrument, from which a chick, 

 also of a mixed nature, will be produced. 



I have used the word contagion above, because Aristotle's 

 view is contradicted by all experience, viz., that a certain part 

 of the embryo is immediately made by intercourse. Neither 

 is it true, as some of the moderns assert, that the vital princi- 

 ple (anima) of the future chick is present in the egg ; for that 

 cannot be the vital principle of the chick which inheres in no 

 part of its body. Neither can the living principle be said 

 either to be left or to be originated by intercourse ; otherwise 

 in every pregnant woman there would be two vital principles 

 (animae) present. Wherefore, until it shall have been deter- 

 mined what the efficient cause of the egg is, what it is of mixed 

 nature that must remain immediately upon intercourse, we may 

 be permitted to speak of it under the title of a Contagion. 



But where this contagion lies hid in the female after inter- 

 course, and how it is communicated and given to the egg, de- 

 mands quite a special inquiry, and we shall have occasion to 

 treat of the matter when we come to discuss the conception of 

 females in general. It will suffice, meantime, if we say that 

 the same law applies to the prime efficient' in which inheres 

 the reason of the future offspring as to the offspring ; as this 

 is of a mixed nature, the nature of its cause must also be mixed; 

 and it must either proceed equally from both parents, or from 

 something else which is employed by both concurrently as in- 

 struments, animated, co-operating, mixed, and in the sexual 

 act coalescing unto one. And this is the third condition of 

 the prime efficient, that it either imparts motion to all the in- 

 termediate instruments in succession, or uses them in some 

 other way, but comes not itself into play. Whence the origin 

 of the doubt that has arisen, whether, in the generation of the 

 chick, the cock were the true prime efficient, or whether there 

 were not another prior, superior to him? For, indeed, all 

 things seem to derive their origin from a celestial influence, 

 and to follow the movements of the sun and moon. But we 

 shall be able to speak more positively of this matter after we 

 haye shown what we understand by the " instrument," or " in- 

 strumental efficient cause," and how it is subdivided. 



