1899] REGENERATION 309 



their flesh to such an extent that the newts die. With small Dytiscidae 

 I have as yet made no experiments, but it is unlikely that the poison 

 serves as a deterrent to them either, and, since they are unable to kill 

 the newts, they are the more likely to injure and eat away certain 

 portions, such as the eye, with their sharp-pointed jaws. A trust- 

 worthy observer informs me that the larva of Dytiscus marginalis 

 seems to go to work on a certain system, for it tries to get at the 

 newt from above, and to attack it on the back just behind the head. 

 Observations specially directed to the point may perhaps determine 

 whether injuries to the eye take place. But even then we should 

 have no proof that the regeneration of the eye is to be regarded as a 

 case of adaptation of the organ to its frequently occurring mutilation. 

 In such cases, however, formal proof is hardly attainable ; it must 

 always be a question of probabilities. "Who, for instance, would 

 attempt to determine how often the beak of the stork is injured ? 

 And, even if this were done say for ten years, over a comparatively 

 large area of the bird's habitat, we should be confronted with the 

 wider and unanswerable question, as to how often such injuries must 

 occur in order that Nature may be prompted to effect, by means of 

 selection, or in some other way, a mechanism of regeneration for the 

 beak. But the mechanism in this case has been established, and for 

 internal organs such as the lungs, oviduct, and vas deferens of newts it 

 has not ; there is therefore a greater probability in the conclusion that 

 regeneration is regulated by adaptation, than in the inference, from 

 the renewal of the leus in Triton, of the presence of a general power 

 of regeneration, — " an adaptiveness not inherited but primary." It 

 will, moreover, be apparent farther on that we have good grounds for 

 assuming that an apparatus for regeneration once established degenerates 

 with exceeding slowness when it has become superfluous. It is thus 

 even conceivable that this apparatus may still persist although no 

 longer necessary in the present conditions of the newt's life. 



That such an apparatus is certainly present in this case is apparent 

 even from the fact, in regard to which all past and present experi- 

 menters are agreed, that the eye of the newt is never regenerated if it 

 be completely excised, and that therefore it is not any kind of cells, 

 but definite cells belonging to the organ itself, which institute the re- 

 generation, as is true in the regeneration of the intestinal canal in 

 pupahood. As I showed in 1864 * in the case of Musca, the intestine 

 during this phase of life breaks down by histolysis and is immediately 

 reconstructed. In 1888 Kowalewsky 2 and van Eees 3 were able to 

 demonstrate in the same insect, and C. Ren gel in 1896 in a beetle, 

 that the new formation had its starting-point in special cells, fairly 

 equally distributed throughout the mucous membrane, which did not 

 break down during pupahood, but on the contrary increased rapidly, 



1 Zcitschr. wiss. Zool. 1864, Bd. xiv. " Op. cit. 18S8, Bd. xlv. 



3 Zoo/. Jahrb. 1888, iii. 



