148 RE GENERA TION 



ear of a good musician becomes more sensitive through practice. If 

 we think of the same stimulus as regularly recurring, and as always 

 answered in the same way, then we may look upon it as a normal 

 condition of the life of the animal and its response as also a normal 

 process in the animal. If, for instance, the breaking into pieces of 

 lumbriculus is a consequence of the approach of cold weather or of 

 other external conditions, then the organization of this animal must 

 react by breaking up in consequence of its adaptation to the condi- 

 tions acquired through heredity. The self-division becomes a normal 

 process under normally recurring conditions. If the organism has 

 been accustomed to respond through numerous generations, and, 

 therefore, its sensitiveness has become highly developed, it will be 

 seen that it may be influenced by the slightest change in the unfavor- 

 able conditions, and although, at first, the change may not be suffi- 

 ciently strong to cause the animal to divide, yet the introductory 

 changes leading to the division may be started, which will in turn 

 make the division, when it occurs, easier and the animal that pos- 

 sesses this responsiveness more likely to survive. This would be the 

 case if a slow process of constriction took place, so that, at the time 

 of separation, no wounds of any size are -formed." " By a further 

 transfer of the phenomenon, a partial, or even a complete, regeneration 

 may set in before division takes place." " We find changes like this 

 in the series of forms, Lumbriculus, Ctenodrilus monostylos, Cteno- 

 drilus pardalis, Nats, Clicstogaster. It appears in a high degree 

 probable that the series has originated in the way described. Per- 

 haps zoologists will find after some thousands of years that lumbricu- 

 lus propagates as does nais at present." In this way von Kennel 

 tries to show how the process of regeneration, that takes place before 

 division, has been evolved from a simple process of breaking up in 

 response to unfavorable conditions. The imaginary process touches 

 on debatable ground, to say the least, at every turn, and until some of 

 the principles involved have been put on a safer basis, it would be 

 unprofitable to discuss the argument at any length. 



We should never lose sight of the fact that the arranging of a series 

 like that beginning with lumbriculus and ending with chaetogaster is a 

 purely arbitrary process and does not rest on any historical knowledge 

 of how the different methods originated or how they stand related, and 

 no one really supposes, of course, that these forms have descended 

 from each other but at most that the more complicated processes may 

 have been at first like those shown in other forms. Even this involves 

 assumptions that are far from being established, and it seems folly 

 to pile up assumption on top of assumption in order to build what is 

 little more than a castle in the air. 



