^^ 



iS95. THE ROLE OF SEX. 197 



be sufficient to bring conjugation about, and we have still to explain 

 why the gametes are of two kinds, female and male ; we have, in fact, 

 to explain why of the two kinds of reproductive gametes the first are 

 large, and are approached by rather than approach the other kind 

 (these we term the female gametes, ova, etc.), while the second are 

 small, actively approach, or are carried by outside agencies to the 

 female gametes (these we term male gametes, sperms, etc.). Now, 

 the utility of this dimorphism will be apparent when we call to mind 

 certain facts in the physiology of the early stages of reproduction. A 

 reproductive cell is a highly differentiated cell ; it contains matter 

 capable of reproducing a new individual, but is devoid of the power 

 of assimilation and nutrition. It has no organs for feeding or digesting 

 food, for then, indeed, it would be fully equipped for all the main 

 purposes of life ; it would be a person or an individual. After it has 

 started away from the parent organism, its life as a gamete must 

 necessarily be short, and every movement it makes, every hour it 

 lives, expends some of its limited potential. When the gametes 

 conjugate, and active development occurs, some time must elapse 

 before organs of nutrition are formed, and all this time capital must 

 be used up, and they must have, one or both of them, a supply of 

 capital at hand. In the case of many animals — the fowl, for instance 

 — the store of capital is very great, and weighs hundreds of times 

 more than that part which directly develops into the chick. The 

 gametes, therefore, not only require to be brought together, but after 

 conjugating, they must start life with sufficient capital. 



If both gametes were motile, and carried each of them a portion 

 of this capital — frequently very abundant — it is evident that a great 

 expenditure of energy would be required. The conditions, actually 

 in existence, where the capital is a part of the quiescent cell and the 

 moving cell only carries its hereditary material, conduce to the saving 

 of energy, and are, therefore, advantageous. In the case of the fowl's 

 egg, no existing cell could propel even a small fraction of its sub- 

 stance ; but leaving such an extreme case, we find that the female 

 gamete, with its store of capital in almost every species that can be 

 named, is many times greater than the male gamete. The advantage 

 of having this store of capital lodged with the quiescent gamete is 

 obvious ; but the dimorphism which we find in nature has other 

 advantages in addition to those just mentioned, and one of the most 

 important appears to me to be the following : — If both sexual cells 

 were similar and motile, conjugation would rarely occur, because it 

 would be impossible to "time" them in their chase for each other. 

 Suppose that a hypothetical individual (A) gives off moving gametes, 

 and that another individual (B) gives off similar gametes, and that new 

 individuals are produced by the conjugation of the gametes of A and 

 B ; unless A and B had some method of timing the formation of 

 these gametes, A might, and probably would, form its gametes at a 

 time when B had none at all. The arrangement that actually obtains 



