THE GERM-PLASM THEORY 83 



which cause particular determinants to vary in a 

 particular manner." ii. 137. 



It will now begin to be clear to the reader that 

 it is possible to explain anything which may be 

 discovered in nature in terms of the " vital unit " 

 theory. On the one hand " the phyletic modifi- 

 cation of the limbs in the ungulates has taken 

 place with striking uniformity in the fore and hind 

 extremities : no animal has ever been one-hoofed 

 in front and two-hoofed behind " (vol. ii. 189). 

 Clearly we have to do with " germ-plasmic corre- 

 lations, and we have assumed from the very first 

 that the different determinants and groups of 

 determinants do indeed stand in definite and close 

 relationship to one another " (vol. ii. 189). On 

 the other hand, we find the kangaroo with remark- 

 ably large and strong hind-limbs and equally 

 remarkably small and weak fore-limbs that is to 

 say, with a striking want of uniformity in his fore 

 and hind extremities. " This, it seems to me, is 

 only possible when amphimixis " of which we 

 have yet to treat " brings about in one individual 

 a favourable coincidence of the chance germinal 

 variations of the determinants of the fore and 

 hind-limbs " (vol. ii. 197). Finally, as a crowning 

 example of what may be done in the way of ex- 

 plaining facts, lumbriculus , of which mention has 

 already been made, can regenerate itself if cut into 

 a number of segments transversely, but cannot 

 regenerate itself if it is divided longitudinally. 



" The reason must lie in the fact that the 

 primary constituents for this kind of regeneration 



