GENESIS. 2H 



tiie mammals or highest T^ertebrata, this homogenesis is in 

 every case yiviparous ; in birds it is uniformly oviparous ; 

 and in reptiles and fishes, it is always essentially oviparous, 

 though there are cases, of the kind above referred to, in 

 which viviparity is simulated. Passing to the Livertehrata, 

 we find oviparous homogenesis universal among the Arach^ 

 nida (except the Scorpions, which are ovo-viviparous) ; 

 universal among the higher Crustacea, but not among 

 the lower ; extremely general, though not universal, among 

 Insects ; and universal among the higher MoUiisca, though 

 not among the lower. Along with extreme inferiority among 

 animals, we find homogenesis to be the exception rather 

 than the rule ; and in the vegetal kingdom, there appear to 

 be no cases, save those of a few aberrant parasites like the 

 Ha^esiacece, in which the centre or axis which arises from a 

 fertilized germ, becomes the immediate producer of fertilized 

 germs. 



Where propagation is carried on by heterogenesis, or is 

 characterized by unlikeness of the successive generations, 

 there is always asexual genesis with occasionally- recurring 

 sexual genesis ; in other words — agamogenesis interrupted 

 more or less frequently by gamogenesis. If w^e set out wdth 

 a generation of perfect males and females ; then, from their 

 ova or seeds, there arise individuals that are neither males 

 nor females, but that produce the next generation from 

 buds. By this method of multiplication, many individuals 

 originate from a single fertilized germ : the product of 

 development is organized round more than one centre or 

 axis. The simplest form of heterogenesis is that 



seen in uniaxial plants. If, as w^e find ourselves obliged to 

 do, we regard each separate shoot or axis of growth, as a dis- 

 tinct individual ; then, in uniaxial plants, the successive in- 

 dividuals are not represented by the series A, A, A, A, &c., 

 like those resulting from homogenesis ; but they are repre- 

 sented by the series A, B, A, B, A, B, &c. For in plants 

 which were before classed as uniaxial (§ 50), and which may 



