8 READINGS IN BIOLOGICAL SCIENCE 



the body causes most of the nutriment to be used up, so that the residue or 

 secretion is small. 



Again, no place has been set apart by Nature for waste-products but 

 they flow wherever they can find an easy passage in the body, but a place 

 has been set apart for all the natural secretions; thus the lower intestine 

 serves for the excretion of the solid nutriment, the bladder for that of the 

 liquid; for the useful part of the nutriment we have the upper intestine, 

 for the spermatic secretions the uterus and pudenda and breasts, for it is 

 collected and flows together into them. The male stands for the effec- 

 tive and active and the female, considered as female, for the passive and 

 it follows that what the female would contribute to the semen of the male 

 would not be semen but material for the semen to work upon. 



So much for the discussion of this question. How is it that the male 

 contributes to generation and how is it that the semen from the male is 

 the cause of the offspring? Does it exist in the body of the embryo as a 

 part of it from the first, mingling with the material which comes from 

 the female? Or does the semen communicate nothing to the material body 

 of the embryo but only the power and movement in it? Now the latter 

 alternative appears to be the right one both a priori and in view of the 

 facts. For, if we consider the question on general grounds, we find that, 

 whenever one thing is made from two of which one is active and the 

 other passive, the active agent does not exist in that which is made, and, 

 still more generally, the same applies when one thing moves and another is 

 moved. It is plain then that it is not necessary that anything at all should 

 come away from the male, and if anything does come away it does not 

 follow that this gives rise to the embryo as being in the embryo, but only 

 as that which imparts the motion and as the form; so the medical art cures 

 the patient. 



What occurs in birds and oviparous fishes is the greatest proof that 

 neither does the semen come from all parts of the male nor does he emit 

 anything of such a nature as to exist within that which is generated, as 

 part of the material embryo, but that he only makes a living creature by 

 the power which resides in the semen. For if a hen-bird is in process of 

 producing wind-eggs and is trodden by the cock before the tgg has 

 begun to whiten and while it is all still yellow, then they become fertile 

 instead of being wind-eggs. And if while it is still yellow she be trodden by 

 another cock, the whole brood of chicks turn out hke the second cock. 



The same conclusion is to be drawn from the generation of oviparous 

 fishes. When the female has laid her eggs, the male sprinkles the milt over 

 them, and those eggs are fertilized which it reaches, but not the others; 

 this shows that the male does not contribute anything to the quantity but 

 only to the quality of the embryo. 



In all animals that can move about, the sexes are separate, one individual 

 being male and one female, though both are the same in species, as with 



