rgS NATURAL SCIENCE. Sept., 



has a very obvious advantage over this conceived condition, for the 

 gametes swim about until they find a large and quiescent form, which 

 is waiting, and can wait an indefinite time for their appearance. In 

 the case of the fish and frog the motile cells are discharged over the 

 quiescent ones, and in the case of the mammal the motile cells are 

 discharged into a duct containing the ova. Here, were the ova 

 motile, there would be less likelihood of their meeting, for they would 

 probably move away from the spot ultimately reached by the motile 

 cells. 



We can see that dimorphism is a necessary corollary of the 

 existence of certain conditions, and we see how, supposing that 

 Volvox, for instance, at one time or another produced several cells all 

 of one kind, any variety of Volvox which developed some of the cells 

 large and quiescent, and others small and motile, would have a distinct 

 advantage, which might lead to the perpetuation of the variety. 



Dimorphism of the gametes permits, we have seen, the act of 

 gametic conjugation to take place in a very economical way, and 

 more economical than if the gametes were similar. We may now 

 very naturally ask whether or not dimorphism plays any other role 

 than that we have assigned to it. This may very likely be the 

 case, but at present it is difficult to find any characters which 

 distinguish all male from all female gametes, other than those already 

 described ; their dimorphism seems to be adapted to economising of 

 energy and nothing more. Of course it is not intended to discuss 

 peculiarities of the gametes special to a species, arising to suit 

 special conditions, but reference is made solely to those points which 

 are of general application. 



In their erudite work on "The Evolution of Sex," Geddes and 

 Thompson, struck with the size and quiescence of the female gamete, 

 and with the small size and frequent activity of the male gamete, 

 view the female as preponderatingly assimilative or anabolic, and the 

 male as preponderatingly katabolic. The female gamete builds up 

 her bigger self; the male gamete uses up the trace of capital he 

 possesses in active mechanical movements. This, of course, implies 

 a constitutional difterence between the two gametes — a building up 

 and a breaking down constitution. It appears to me very doubtful 

 whether the evidence, taken as a whole, points in this direction, and 

 for the following reasons. Many gametes — pollen-grains, for instance 

 — do not possess the power of movement. They are inert masses, 

 small in size, and carried by the wind or by the aid of insects. We 

 have no reason to suppose them more katabolic than the ovules, 

 unless we have indication of this in the presence of tissue metabolites, 

 or unless we have evidence of active protoplasmic movement which 

 we know must result in metabolites. This evidence is wanting, or, 

 at any rate, very incomplete, and we cannot fall back upon their 

 smaller size ; for though smaller, it by no means follows that they are 

 more katabolic. The most katabolic cells in the body are, perhaps, 



