Zoological Prohlems for Natural History Society. 7 



whip-like lash. This species is most abundant along the 

 north shore as far as Lachine. Canibarus Bartonii, on the 

 other hand, is always of a light red color : it has markedly 

 smaller eyes, a broad, blunt rostrum without spines at the 

 edge, and the first abdominal leg of the male ends in 

 a liook. Canibarus Bartonii is much rarer than the other 

 species, so far as my experience goes. I have found 

 single specimens everywhere, but it appears to be 

 abundant in the late fall on the back river (Ottawa.) It 

 would be a most interesting problem to try to determine 

 the distribution of these two species, and, if possible, 

 tlieir habits. Faxon, who has made a study of the ISTorth 

 American Astacidae, places the two species in two 

 different sections of the genus Canibarus, but he has 

 no observations on their habits. 



Another most interesting question which inevitably 

 arises when we find two species of one genus living 

 side by side is what prevents them from intermingling. 

 The only proper definition of a species is a group of 

 individuals closely resembling one another and breeding 

 with one another so as to produce fertile offspring. Now 

 when the naturalist separates two varieties as distinct 

 species, he is seldom able to bring proof that they will not 

 interbreed with one another. Hence the vast majority of 

 determinations of species are mere surmises, surmises 

 based on the belief that the only thing which will cause 

 a group of animals to remain similar to one another is 

 constant interbreeding. This is all very well in cases 

 where the species are as distinct as our si^ecies of 

 Cambarus, but in very many cases the differences 

 separating allied species are so slight that there is the 

 strongest reasons for ■ doubting whether, in the true and 

 physiological sense, they are distinct. 



It would be comparatively easy to cross Cambarus 

 virilis and C. Bartonii in the spring, and the animals 

 experimented on could be kept either in a small pond or 

 in little aquaria. 



