318 DISTRIBUTION AND AETIOLOGY OF THE CRAYFISHEa 



operations, by what is commonly termed Creation; or we 

 must seek for it in conditions afforded by the usual 

 course of nature, when the hypothesis assumes some 

 shape of the doctrine of Evolution. And there are two 

 furms of the latter hypothesis ; for, it may be assumed, 

 on the one hand, that crayfishes have come into exist- 

 ence, independently of any other form of living matter 

 which is the hypothesis of spontaneous or equivocal 

 generation, or abiogenesis ; or, on the other hand, 

 we may suppose that crayfishes have resulted from the 

 modification of some other form of living matter ; and 

 this is what, to borrow a useful word from the French 

 language, is known as transformism. 



I do not think that any hypothesis respecting the 

 origin of crayfishes can be suggested, which is not 

 referable to one or other of these, or to a combination 

 of them. 



As regards the hypothesis of creation, little need be 

 said. From a scientific point of view, the adoption of 

 this speculation is the same thing as an admission that 

 the problem is not susceptible of solution. Moreover, 

 the proposition that a given thing has been created, 

 whether true or false, is not capable of proof. By 

 the nature of the case direct evidence of the fact is 

 not obtainable. The only indirect evidence is such 

 as amounts to proof that natural agencies are incom- 

 petent to cause the existence of the thing in question. 

 But such evidence is out of our reach. The most that 



