REGENERATION I 2 5 



an animal. Some statements which have been made on this 

 subject seem hardly to admit of any but the latter explanation. 

 Thus, according to Spallanzani, the jaw of a Triton may become 

 regenerated along with its bones and teeth. Bonnet states that 

 even the eye of this animal is replaced after it has been extir- 

 pated. It has never come before my notice that in the natural 

 state Tritons frequently lose the lower jaw in combat : but some 

 of these animals which I had put for a short time in a small 

 vessel attacked each other vigorously, and several times one of 

 them seized another by the lower jaw, and tugged and bit at it 

 so violently that it would have been torn off if I had not sepa- 

 rated the animals. The loss of part of the jaw or eye may 

 therefore occur not infrequently in the natural state, and we may 

 thus perhaps assume that these parts are adapted for regenera- 

 tion. Kennel, moreover, gives an account of a stork, the upper 

 beak of which had accidentally been broken off in the middle, 

 the lower one then being sawn off to the same length, and both 

 were subsequently regenerated. Such cases, the accuracy of 

 which can scarcely be doubted, indicate that the capacity for 

 regeneration does not depend only on the special adaptation of 

 a particular organ, but that a general power also exists which 

 belongs to the whole organism, and to a certain extent affects 

 many, and perhaps even all, parts. By virtue of this power, 

 moreover, simpler organs can be replaced even when they are 

 not specially adapted for regeneration. 



From our point of view, such cases are not incomprehensible 

 in principle. We need only assume that in all, or at any rate 

 in many, of the nuclear divisions in the embryo, some of the 

 earlier determinants remain associated with later generations 

 of cells as accessory idioplasm. It only remains to trace this 

 arrangement — which is a more or less universal one, and affects 

 the whole body — to its origin ; for no arrangement can be pro- 

 duced wiiich is not useful, especially when it concerns such a 

 complicated mechanism as that for supplying the idioplasm with 

 accessory determinants. We are therefore led to infer that tJtc 

 general capacity of all parts for regeneration may have been 

 acquired by selection in the lower and simpler forms, and that 

 it gradually decreased in the course of phytogeny in correspond- 

 ence with the increase in complexity of organisatio7i ; but that it 

 may, on the other hand, be increased by special selectii>e processes 

 in each stage of its degeneration, in the case of certain parts 



