DEVELOPMENT AND GENESIS. 463 



cellular Algce that shed their tetraspores, the Archegoniates 

 that spontaneously separate their fronds or drop their gem- 

 ma?, show us an extra mode of multiplication which, among 

 flowering plants, is exceptional. This extra mode of multipli- 

 cation among these simpler plants, is made easy by their low 

 development. Tetraspores arise only where the frond con- 

 sists of untransformed cells; gemma? bud out and drop off 

 only where the tissue is comparatively homogeneous. 



Should it be said that this is but another aspect of the 

 antagonism already set forth, since these undeveloped forms 

 are also the smaller forms; the reply is that though in part 

 true this is not wholly true. Various marine Algce which 

 propagate asexually, are larger than some Phaenogams which 

 do not thus propagate. The objection that difference of 

 medium vitiates this comparison, is met by the fact that it is 

 the same among land-plants themselves. Sundry of the low- 

 ly-organized Liverworts which are habitually gemmiparous, 

 exceed in size many flowering plants. And the Ferns show 

 us agamic multiplication occurring in plants which, while 

 they are inferior in complexity of structure, are superior in 

 bulk to numbers of annual Monocotyledons and Dicotyledons. 



§ 345. In the ability of the lowly-organized substance of a 

 Sponge to transform itself into mu]titudes of gemmules, we 

 have an instance of this same direct relation in the animal 

 kingdom. Moreover, the instance yields very distinct proof 

 of an antagonism between development and genesis, inde- 

 pendent of the antagonism between growth and genesis; 

 for the Sponge which thus multiplies itself asexually, as well 

 as sexually, is far larger than hosts of more complex animals 

 which do not multiply asexually. 



Once again may be cited the creature so often brought in 

 evidence, the Hydra, as showing us how rapidity of agamic 

 propagation is associated with inferiority of structure. Its 

 power to produce young ones from nearly all parts of its 

 body, is due to the comparative homogeneity of its body. In 



