without that which confers fecundity. All of these matters we shall advert to after we have shown what and how two principles, male and female, concur in the production of the egg and the process of generation, and in what way both may be regarded as efficient causes and parents of the egg.
EXERCISE THE THIRTY-FIRST.
The egg is not produced by the cock and hen in the way Aristotle would have it.
It is certain, as we have said, that a fruitful egg is not pro- duced without the concurrence of the cock and hen ; but this is not done in the way that Aristotle thought, viz. by the cock as prime and sole ' agent/ the hen only furnishing the ' matter/ Neither do I agree with him when he says z 1 " When the semen masculinum enters the female uterus, it coagulates the purest portion of the catamenia ;" and shortly afterwards : " but when the catamenia of the female has set in the uterus, it forms, with the semen masculinum, a coagulum like that of milk ; for curd is milk containing vital heat, which attracts like particles around it, and combines and coagulates them ; and the semen of the male (genitura) bears the same affinity to the nature of the catamenia. For milk and the menstrual dis- charge are of the same nature. When coagulation has taken place, then an earthy humour is excreted and is drawn around, and the earthy portion drying up, the membranes are produced both as matter of necessity, and also for a certain purpose. And these things take place in the same manner in all creatures, both oviparous and viviparous."
But the business in the generation of an egg is very different from this; for neither does the semen, or rather the ' geniture/ proceeding from the male in the act of intercourse, enter the uterus in any way, nor has the hen, after she conceives, any particle of excrementitious matter, even of the purest kind, or any blood in her uterus which might be fashioned or perfected by the discharge of the male. Neither are the parts of the egg,
1 De Gen. Anim. lib. ii, cap. 4.
