3 o8 AUGUST WEISMANN [april 



that the argument based on this case remained unchallenged. From 

 Calucci's experiment of extracting the lens in Triton, which resulted, 

 as was expected, in regeneration, G. Wolff 1 inferred that there was 

 here " a new adaptiveness appearing for the first time," since it is 

 " impossible that regeneration can take place in accordance with the 

 inherited mode of its ontogenetic origin." The latter conclusion is 

 indeed correct, but the former one does not follow from it, and it seems 

 to me quite out of the question to bring forward this case as contra- 

 dictory to the view that regeneration depends upon a special inherited 

 adaptation. It will, of course, be readily admitted that newts, in their 

 natural conditions of life, are not liable to excision of the lens, but it 

 does not necessarily follow that the lens in these amphibians cannot be 

 adapted for regeneration, for at any rate it may be lost along with 

 other portions of the eye. As far back as 1781, Bonnet and Blumen- 

 bach showed that the eye of newts would renew itself completely 

 even when all of it except a small portion (according to Blumenbach, 

 as little as one-fifth of the bulb) was extirpated, and the more recent 

 observations of Philippeaux (1880) have confirmed these conclusions. 

 This regeneration certainly appears to us especially remarkable, since 

 it necessarily presupposes quite a different mode of formation of the 

 eye from that which takes place in the embryo. Leaving out of 

 account altogether the question as to whether we are or are not in a 

 position to form a theoretical conception of the phyletic origin and 

 the nature of this process, it is at any rate certain that some sort of 

 mechanism for the regeneration of the eye exists. But if this is true 

 for the tvhole eye, why should we be surprised that a 'part of it, the 

 lens alone, may be regenerated. A single toe of the newt's foot, if 

 cut off, will grow again just as well as a whole leg. 



There is no doubt, however, that the eye of Triton is susceptible of 

 injury, and that it is frequently injured in natural conditions. Even 

 newts fight among themselves, and I have elsewhere shown 2 that these 

 animals, at anyrate in the breeding-season, ferociously attack and injure 

 one another. I once put a number of newts together for a short time 

 in a small empty glass, and I then saw that the animals attacked each 

 other furiously, biting and struggling pertinaciously. " Several times 

 one seized another by the lower jaw and tugged at it so violently that 

 it would have been torn out if I had not forcibly separated the animals." 

 From this I concluded that " the loss of part of a jaw or eye may 

 therefore not infrequently occur in the natural state," and I may now 

 add that the newt is liable to attacks by water-beetles of the family 

 Dytiscidae. I was for a time uncertain whether the powerful poison 

 which newts, like toads, secrete from the skin was any protection 

 against such attacks, but this is not the case. Large Dytiscidae attack 

 the newts whenever they can find no other food, and they eat away 



1 Arch. Kill ic Iclcclungsmechanik, Bd. i. p. 380. 



2 " Keimplasma," p. 167. (Eng. Ed. p 125.) 



