416 APPENDIX 



of the most varied injuries, and can be artificially divided, 

 multiplied by division. This conception is connected with 

 and is indispensable to the other conception, that the animal 

 as distinguished from the plant possesses an indivisible soul. 



In consequence of this conception, the greatest astonish- 

 ment was excited when in the middle of the last century 

 Trembley showed that a small insignificant but genuine 

 animal, the Hydra or fresh- water polyp, which lives in our 

 waters, could be cut up into quite small pieces in the most 

 various directions, with the result that each piece grew into a 

 new perfect individual. These experiments attracted the great- 

 est notice, not only from naturalists, but also from philosophers 

 and theologists, on account of their bearing on the question 

 of the indivisibility of the soul. 



The philosopher Bonnet and others repeated the experi- 

 ments of Trembley, and extended them to other animals, 

 especially to a small worm which likewise lives in our fresh 

 waters, the Nais proboscidea, an animal which resembles the 

 earth-worm in form and is allied to it. It was found that 

 when this worm is cut transversely into several portions each 

 part goes on living after the division. But it was also found 

 that this worm multiplies by dividing itself in exactly the 

 same way as it can be divided artificially. 



But it must be pointed out that the conditions are different 

 in the two cases. The whole Hydra can be cut up in all 

 directions ; but in the worm there are a number of segments 

 in linear series which are to a certain degree independent — 

 the rings of the body, — and subdivision cannot go beyond the 

 separation of these without endangering the life of the parts. 



But the physiological treatment of zoology has in recent 

 times been extraordinarily neglected, in my opinion, to the 

 great injury of the science; and such physiological experiments 

 were not for a long time continued. It struck me as very 

 desirable to try experiments of a similar kind, for it seemed 



