BIOLOGICAL BEGINNINGS 7 



that live by clinging to something else, inasmuch as their nature resembles 

 that of plants, have no sex any more than plants have, but as applied to 

 them the word is only used in virtue of a similarity and analogy. For there 

 is a slight distinction of this sort, since even in plants we find in the same 

 kind some trees which bear fruit and others which, while bearing none 

 themselves, yet contribute to the ripening of the fruits of those which do, 

 as in the case of the fig-tree and the caprifig. 



The same holds good also in plants, some coming into being from seed 

 and others, as it were, by the spontaneous action of Nature, arising 

 either from decomposition of the earth or of some parts in other plants, 

 for some are not formed by themselves separately but are produced upon 

 other trees, as the mistletoe. 



Some animals manifestly emit semen, as all the sanguinea, but whether 

 the insects and cephalopoda do so is uncertain. Therefore this is a question 

 to be considered, whether all males do so, or not all; and if not all, why 

 some do and some not; and whether the female also contributes any semen 

 or not; and, if not semen, whether she does not contribute anything else 

 either, or whether she contributes something else which is not se- 

 men. 



Now it is thought that all animals are generated out of semen, and that 

 the semen comes from the parents. In this investigation and those which 

 follow from it, the first thing to do is to understand what semen is, for 

 then it will be easier to inquire into its operation and the phenomena con- 

 nected with it. Now the object of semen is to be of such a nature that from 

 it as their origin come into being those things which are naturally formed, 

 not because there is any agent which makes them from it . . . but simply 

 because this is the semen. 



Now the offspring comes from the semen and it is plainly in one of the 

 two following senses that it does so — either the semen is the material from 

 which it is made, or it is the first efficient cause. Now that which comes 

 from the generating parents is called the seminal fluid, being that which 

 first has in it a principle of generation, in the case of all animals whose 

 nature is to unite; semen is that which has in it the principles from both 

 united parents, as the first mixture which arises from the union of male 

 and female, be it a foetus or an ovum, for these already have in them that 

 which comes from both. 



Semen, then, is part of a useful secretion. So we must say the opposite 

 of what the ancients said. For whereas they said that semen is that which 

 comes from all the body, we shall say it is that whose nature is to go to 

 all of it, and what they thought a waste product seems rather to be a secre^ 

 tion. 



A further proof that it is not a waste product, but rather a secretion is the 

 fact that the large animals have few young, the small many. For the 

 large must have more waste and less secretion, since the great size of 



