290 DISTRIBUTION AND .ETIOLOGY OF THE CRAYFISHES. 



or *• stone crayfish," and the latter by that of " Eclel- 

 krebs," or " noble crayfish." 



Milne Edwards, it will be observed, sjieaks of these 

 two forms of crayfish as " varieties " of the species 

 Astacus Jiuviatilis ; but, even as far back as the year 

 1803 some zoologists began to regard the "stone cray- 

 fish " as a distinct species, to which Schrank api^lied the 

 name of Astacus torrentmm, while the " noble crayfish " 

 remained in possession of the old denomination, Astacus 

 Jiicviatilis ; and, subsequently, various forms of " stone- 

 crayfishes " have been further distinguished as the sj)ecies 

 Astacus saxatilis, A. tristis, A. pall'ijies, A. fontinaUs, 

 kc. On the other hand, Dr, Gerstfeldt,* who has devoted 

 esj)ecial attention to the question, denies that these 

 are anj'thing more than varieties of one species ; but he 

 holds this and Milne Edwards's " second variety " to be 

 specifically distinct from one another. 



We thus find ourselves in the presence of three views 

 respecting the English and French crayfishes. 



1. They are all varieties of one species — A. Jiuviatilis. 



2. There are two species — A. jiuviatilis, and A. tor- 

 rentium, of which last there are several varieties. 



3. There are, at fewest, five or six distinct sjiecies. 

 Before adopting the one or the other of these 



views, it is necessary to form a definite conception of 

 the meaning of the terms " sjiecies " and "variety." 



* " Ueber die Flu6skrebse Europas." Mem. de I'Acad. de St. Peters- 

 burg, 1859. 



