d 



1 6 AUGUST WEISMANN [april 



stimulus to the femur — when it is pinched, crushed, or cut through 

 the middle : only in this region does autotomy occur. 



Bordage states that the act of emerging from the egg may result 

 in the loss of the tarsi and their subsequent regeneration, for it 

 frequently happens that the insect does not succeed in freeing one of 

 its legs from the egg-shell, which it is obliged to drag about to the 

 great hindrance of its progress, until it is finally stopped entirely by 

 the catching of the shell on some object. In such a case the insect 

 struggles with all its might to free itself, and in doing so not infre- 

 quently loses the tarsus. 



Something similar takes place during the process of ecdysis, for 

 it frequently happens that the insect remains entangled in the old 

 skin. Of a hundred Phasmids nine died in this way during moulting, 

 while twenty-two tore themselves free with the loss of one or more 

 legs, and only sixty-nine survived the process without loss. 



Obviously, then, the power of autotomy with subsequent regenera- 

 tion is here a frequently-used and advantageous arrangement ; but I 

 cannot agree with Bordage in regarding the pulling and struggling of 

 the insect in the effort to free itself from the encumbering skin as 

 the directly operating cause of the fusion of femur and trochanter 

 which gives rise to the breaking-point adapted to autotomy. Even if 

 this pulling and struggling lasted for a whole day, it is extremely 

 doubtful that it could induce anchylosis of the joint ; and if it could, 

 it would be impossible that the anchylosis should be transmitted, and 

 that it should thus form the basis of a general and transmissible fusion 

 of the joint ; for how could a variation of the joint influence the eggs 

 or sperm-cells of the insects ? 



The facts communicated by Bordage are especially of value, because 

 they show that it is not only the enemies of the insect in question 

 that have a part to play in the development of the tendency to autotomy 

 and regeneration, as has hitherto been thought : other events are also 

 concerned which are of general occurrence and are repeated several 

 times in the ordinary course of life, viz. the moultings. It is not 

 impossible that the ecdyses of crustaceans operate in a similar way, 

 but no precise statement on this point can be made without fresh 

 investigations. 



With regard to the phyletic origin of the adaptations in question, 

 Bordage supposes that the capacity for regenerating the tarsus, the 

 lower end of the tibia, and the whole leg from the suture has been 

 derived from autotomy, which, again, he believes to have been brought 

 about by persecution on the part of the saurians and batrachians of 

 primeval times (Stegocephala). I prefer, on the contrary, to regard 

 the power of regeneration as the older capacity, and autotomy as 

 derived from it ; for I doubt whether any part could regain the 

 power of regeneration if it, or the parts from which it is phyletically 

 descended, had once lost this power. In my opinion, therefore, the 



