GENESIS. xJi7 



fost, in the production of new individualities. To the 



last, however, there is of necessity a greater or less disinte- 

 gration. The seeds and pollen -grains of' a flowering plant, 

 are disintegrated portions of tissue ; as are also the ova and 

 spermatozoa of animals. And whether the fertilized germs 

 carry away from their parents small or large quantities of 

 n:itriment, these quantities of nutriment in all cases involve 

 further negative or positive disintegrations of the parents. 



New individuals that result from agamogenesis, usually do 

 not separate from the parent-individuals, until they have 

 undergone considerable development, if not complete develop- 

 ncent. The agamogenetic offspring of those lowest organisms 

 wliich develop centi'ally, do not, of course, pass beyond cen- 

 tral structure ; but the agamogenetic off'spring of organisms 

 that develop axially, commonly assume an axial structure 

 before they become independent. The vegetal kingdom shows 

 us this in the advanced organization of detached bulbils, and 

 of buds that root themselves before separating. Of animals, 

 the Hydrozoa, the Trematoda, the Salpce^ and the Aphides^ 

 present us with different kinds of agamogenesis, in all of 

 which the new individuals are organized to a considerable 

 extent before being cast off. This rule is not without excep- 

 tions, however. The winter-eggs of the Plumatella^ developed 

 in an unspecialized part of the body, present us with a case 

 of metagenesis, in which centres of development, instead oi 

 axes, are detached ; and in the above-described parthenogene- 

 sis of moths and bees, such centres are detached from an 

 ovarium. 



When produced by gamogenesis, the new individuals be- 

 come independent of the parents while in the shape of centres 

 of development, rather than axes of development ; and this 

 even where the reverse is apparently the case. The fertilized 

 germs of those inferior plants which are central, or niulticen- 

 tral, in their development, are of course thrown off as centres. 

 In the higher plants, of the two elements that go to the form- 

 ation of the fertilized germ, the pollen-cell is absolutely 

 15 



