1 92 BIOLOGICAL LECTURES. 



that is in question, but its power to regenerate after injury. 

 In this I agree with Weismann, for it is no more evident how 

 a series of injuries in succeeding generations could finally bring 

 about complete regeneration than that the result should follow 

 after one injury. If after the first injury, then, there is no need 

 of any theory of inheritance. 



Weismann believes, however, that the power of regeneration 

 is under the guidance of " Natural Selection." His argument, 

 as far as I understand it, is this : Of all the animals injured in 

 each generation, those that regenerate better are more likely 

 to survive ; and since in each species certain organs are more 

 liable to injury than others, the selection will take place mainly 

 in respect to these parts ; hence they possess the power of 

 regeneration. Other organs of the body not subject to frequent 

 injury do not show the power of regeneration, either because, 

 having once had it, it has been gradually lost (through panmixia), 

 or because the process has never been acquired in these organs. 

 It may be pointed out, in passing, that since the limb of a newt 

 and the tail of a tadpole regenerate at every level, and regen- 

 erate the kind of limb peculiar to that particular species, we 

 must conclude, on Weismann's hypothesis, that this power has 

 been acquired through selection for every possible level. The 

 demand made on our credulity is enormous. 



Weismann has made other statements in his book on the 

 Germ Plasm, and in a later paper ('99) entitled " Regeneration : 

 Facts and Interpretations," that are worth examining. In the 

 former he says : " It may, I believe, be deduced with certainty 

 from those phenomena of regeneration with which we are 

 acquainted that tJie capacity for regeneration is not a primary 

 quality of the organism, but that it is a phenomenon of 

 adaptation." Again: "Hence there is no such thing as a 

 general power of regeneration ; in each kind of animal this 

 power is graduated, according to the need of regeneration, in 

 the part under consideration." "We are, therefore, led to infer 

 that the general capacity of all parts for regeneration may have 

 been ACQUIRED BY SELECTION a in the lower and simpler forms, 

 and that it has gradually decreased in the course of phylogeny, 



1 The italics are my own. 



