THE LIBERATION OF SPECIAL GERM CELLS. 51 



organism are inherent. This is the primary characteristic 

 of sexual, as opposed to asexual multiplication. 



It is also conceivable that organisms might have remained 

 approximately like one another in constitution, and at all 

 times very nearly the same, and that they might have 

 liberated similar germ cells capable of immediate develop- 

 ment. Such a race would have illustrated the one charac- 

 teristic of sexual reproduction, the liberation of special germ 

 cells, but it would have been without that other characteristic 

 of sexual reproduction, — the existence of dimorphic germ 

 cells, of different kinds of sexual organs, or of male and 

 female individuals. 



The Liberation of Special Germ Cells. 



One must think of this as an economical improvement on 

 the method of starting a new life by asexual overgrowth or 

 by the liberation of buds. Asexual reproduction, as Spencer 

 and Hseckel point out, is a mode of growth in which 

 the bud, or whatever it is, becomes discontinuous from the 

 parent. The buds of a sponge, of a coral, of a sea mat 

 (Polyzoon), or of many Tunicates, remain attached to the 

 parent. If there be a keen struggle for subsistence, this 

 may be disadvantageous ; but in some cases, doubtless, the 

 colonial life which results is a source of strength. In the 

 case of Hydra, however, the buds are set adrift ; the same 

 is true of not a few worms. This liberation of buds takes 

 us nearer the sexual process of liberating special germ cells. 

 But unless the organism is in very favourable nutritive 

 conditions, in which overgrowth is natural, the liberation of 

 buds is evidently an expensive way of continuing the life of 

 a species. Not only so, but we can hardly think of budding 

 even as a possibility in very complex organisms, like snails 

 or birds, in which there is much division of labour. More- 

 over, the peculiarity of a true germ cell is, that it is un- 

 specialised, continuous in quality vi^ith the original germ cell 

 from which the parent arose, and not very liable to be 

 tainted by the mishaps which may befall the "body" which 

 bears it. And, finally, in the mixture of two units of living 

 matter which have had different histories, the possibility of 

 permutations and combinations, in other words, of variation 



