GENERATION OF ANIMALS, I. xix. 



no pleasure from the act of coitus ; and, on the con- 

 trary side, when the female derives as much pleasure 

 as tile male, and they both keep the same pace, the 

 female does not bear — unless there is a proper amount 

 of menstrual Uquid (as it is called) present. Thus, 

 the female does not bear (a) if the menstrual fluid is 

 completely absent, (6) if it is present and the dis- 

 charge of moisture is in progress (in most instances) ; 

 but only (c) after the evacuation is over. The reason 

 is that in one case (a) the female has no nourishment, 

 no material, for the dynamis " supplied by the male 

 in the semen to draw upon and so to cause the living 

 creature to take shape from it ; in the other case 

 (6) it is washed right away owing to the volume of 

 the menstrual fluid. When, however, (c) the dis- 

 charge is over and most of it has passed off, then what 

 remains begins to take shape as a fetus. There are 

 instances of women who conceive without the 

 occurrence of menstrual discharge ; others conceive 

 during its occurrence but not after it. The reasons 

 are these. The former produce only just so much 

 liquid as remains in fertile individuals ^ after the 

 evacuation is over, and there is no surplus residue to 

 be discharged externally ; in the latter, the mouth 

 of the uterus closes up after the evacuation is over. 

 Therefore, when there has been a plentiful discharge 

 and yet the evacuation still continues, though not so 

 copiously that the discharge of moisture carries the 

 semen away with it, that is the time when if they 

 have intercourse women can conceive again. There 

 is nothing odd about the menstrual fluid's continuing 

 to flow after conception has taken place ; indeed it 

 actually recurs afterwards up to a point, but it is 

 scanty and does not last throughout gestation. How- 



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