422 APPENDIX 



mammals, including man, are not simple individuals ; 

 our bodies are transversely segmented. In the course 

 of evolution, it is true, amalgamation or concentration has 

 proceeded to a very higli degree, at least in the highest 

 animals ; but in the lower forms of the vertebrata this is 

 scarcely carried further than is the case in the Arthropoda, 

 especially in insects. The central points towards ^vhich the 

 segments have been united appear plainly when we attempt 

 to divide these animals also in different directions. Insects 

 can be divided with the result that the separate parts, e/j. 

 the posterior part of a stag-beetle, retain for a long time 

 an independent life — a very long time if they are pro- 

 tected from desiccation. The same holds also for verte- 

 brates ; for w^e can cut off the head of a frog and the 

 remaining part of the nervous system retains its functional 

 activity. It seems to me certain, notw^ithstanding the con- 

 trary view which still prevails, that voluntary action in this 

 animal proceeds also from parts of the spinal cord ; for after 

 the head has been cut off the creature evidently acts quite 

 consciously. A tortoise, it is also known, can survive de- 

 capitation for a long time, and apparently likewise responds 

 voluntarily to external stimuli. The higher we ascend in the 

 animal scale, the less do we find separated parts capable of 

 surviving, and the more does that possibility of recrescence 

 disappear which still exists in the lower vertebrates, in which, 

 for instance, legs or tails are reproduced when lost. In our- 

 selves, traces of this power of recrescence still remain in the 

 formation of scars, and in the reattachment of certain parts 

 which are restored to their place immediately after they have 

 been separated from the body. 



Our subject can also be illustrated by facts of the reverse 

 kind. As in the cases mentioned, a differentiation and union of 

 equivalent parts produced a compact and co-ordinated whole 

 — individuals, as it were, being specialised into organs — so in 



