KEPRODUCTION BY GERM-CELLS 273 



from place to place is only a visible outcome, fertilization was pictm^ed, 

 by a not very luminous process of reasoning, as the awakening of life 

 in the ovum — in itself incapable of further life — through the trans- 

 ference to it of movement through the agency of the zoosperm. Some 

 investigators even went the length of regarding the ovum as ' dead 

 organic material.' 



I mention this at this point, though I do not propose in the 

 meantime to inquire further into the significance of the conjugation 

 of the sex-cells. But the view just referred to is so completely refuted 

 even by the external form of the male germ-cells in many groups of 

 plants and animals, that I cannot discuss these differences in form 

 without at the same time indicating the conclusions which they 

 directly suggest. 



The great majority of plants and animals exhibit the zoosperm 

 form of male germ-cells, and this must obviously be interpreted in 

 the light of the fact that the ova to be fertilized are not generally to 

 be found in direct proximity to the sperms shed by the male organism, 

 but are at some distance from them. Among MedussB and Polyps both 

 male and female germ-cells are liberated into the water, simultaneously 

 it may be, but separated from each other by distances of some feet or 

 yards. The spermatozoa then swim about seeking the ova, which 

 are also floating freely in the sea, guided by a power of attraction on 

 the part of the latter — an attraction of whose nature we know nothing, 

 though in the case of certain, fern-ova it has been traced to the 

 secretion of malic acid (Pfeffer). 



The same conditions obtain among Sponges. Here, again, the 

 persons or stocks are either male or female ; the latter produce large 

 delicate ova, which lie in the interior of the sponge and there await 

 the fertilizing sperms ; the former give off the ripe sperms into the 

 water in such abundance that thousands and millions of zoosperms 

 burst forth simultaneously in all directions ; these seek about for 

 a female sponge, penetrate into its canal system, and so ultimately 

 reach the ova. Of course only a very few of them reach their goal ; 

 the greater number are lost in the water and become the prey of 

 Infusorians, Radiolarians, or other lowly animals. The fact that 

 enormous numbers thus miss their true aim shows us why these 

 zoosperms must be produced in such quantities ; it is simply an 

 adaptation to the extraordinarily high ratio of elimination in these 

 cells, just as the number of young annually produced by an animal, 

 or of seeds by a plant, is regulated by natural selection according to 

 the ratio of elimination of the particular species. The more numerous 

 the descendants which succumb each time to unfavourable circum- 

 I. S 



