276 THE inductio:ms of biology. 



plication.* There is, however, nothing for us but a choice of 

 imperfections. We cannot by any logical dichotomies accu- 

 rately express relations which, in Nature, graduate into one 

 another insensibly. Neither the above, nor any other scheme, 

 can do more than give an approximate idea of the truth. 



§ 76. Genesis under every form is a process of negative 

 or positive disintegration; and is thus essentially opposed to 

 that process of integration which is the primary process in 

 individual evolution. Negative disintegration occurs in those 

 cases where, as among the compound Hydrozoa, there is a 

 continuous development of new individuals by budding from 

 the bodies of older individuals; and where the older indi- 

 viduals are thus prevented from growing to a greater size, or 

 reaching a higher degree of integration. Positive disintegra- 

 tion occurs in those forms of agamogenesis where the produc- 

 tion of new individuals is discontinuous, as well as in all cases 

 of gamogenesis. The degrees of disintegration are various. 

 At the one extreme the parent organism is completely broken 

 up, or dissolved into new individuals; and at the other 

 extreme each new individual forms but a small deduction 

 from the parent organism. Protozoa and Protophyta show 

 us that form of disintegration called spontaneous fission: 

 two or more individuals being produced by the splitting-up 

 of the original one. The Volvox and the Hydrodictyon 

 are plants which, having developed broods within themselves, 

 give them exit by bursting; and among animals the one 

 lately referred to which arises from the Distoma egg, entirely 

 loses its individuality in the individualities of the numerous 



* Prof. Huxley avoids this difficulty by making every kind of Genesis a 

 mode of development. His classification, which suggested the one given 

 above, is as follows : — 



f Growth 

 ' Continuous ■{ 



[^ Metamorphosis 



Development ■< 



f Metagenesis 



f Agamogenesis -l 

 ^ Discontinuous -{ [ Parthenogenesis 



1^ Gamogenesis 



