were a fetation.^a (By fetation I mean the primary mixture of male and female.) This explains incidentally why one body only is formed from one seed—e.g., one stalk from one grain of corn, just like one animal from one egg (double-yolked eggs of course count as two eggs). In those groups, however, where male and female are distinct, many animals may be formed from one semen, which suggests that the nature of semen in animals differs from that in plants.^b We have as a proof of this those animals which are able to produce more offspring than one at a time, where more than one are formed as the result of one act of coitus. This shows also that the semen is not drawn from the whole body; because we cannot suppose (a) that at the moment of discharge it contains a number of separate portions from one and the same part of the body; nor (b) that these portions all enter the uterus together and separate themselves out when they have got there.^c No; what happens is what one would expect to happen. The male provides the “form” and the “principle of the movement,”^d the female provides the body, in other words, the material.^e Compare the coagulation of milk. Here, the milk is the body, and the fig-juice or the rennet contains the principle which causes it to set.^f The semen of the male acts in the same way as it gets divided up into portions within the female. (Another part of the treatise^g will explain the Cause why in some cases it gets divided into many portions, in others into few, while in others it is not divided up at all.) But as this semen which gets divided up exhibits no difference in kind, all that