ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 503 



cant ones in C. monongaletms. The same is true of C. diogenes, leaving out of 

 account the differences between the eastern and western forms. The most important 

 variation is that of the width of the areola. In this there is a tendencj' toward 

 regional restriction, but it is not complete. The wide areola, being a more primi- 

 tive character, does not represent the variation, but the original condition, whioii is 

 retained only in a small part of the range and is even there not general. It is a 

 character that has a tendency to disappear and may be classed under atavism. A 

 case of albinism has been observed in C. diogenes. 



The conclusions from the above observations are that in the Cambarus forms of 

 Pennsylvania the morphological characters are very constant, and that the varia- 

 tions observed are generally only slight, diverging very little from the typical condi- 

 tions. Anything that looks like a " mutation " in De Vries' sense is entirely un- 

 known, for the cases of hermaphroditism camiot be regarded as such, and the cases 

 of atavism and albinism do not fall under it, being clearly of a " retrograde " char- 

 acter (De Vries, 1905, p. 121 ci seq.). 



Further, even between most of our well established species differences are so 

 slight that they cannot be regarded as representing " mutations," that is to say, 

 sudden leaps in a progressive direction (De Vries, /. c, p. 141 ). This is most evident 

 in tlio projnnquus-section, where the three forms, two of which at least must be re- 

 garded as species, are distinguished by such insignificant charactei-s that it is impo.s- 

 sible to talk of "leaps" or of "sudden changes." The same is true of the differ- 

 ences of C. carolinus, C. 'iiioiiongahnms, and C. diogeitci^, the amount of the differences, 

 although well marked, being very small, and the " gaps " between these species be- 

 ing infinitesimal. The only striking difference is in color, but before we know what 

 causes the appearance of various colors we cannot express any judgment on this 

 point. 



Even in those species which are more isolated from the rest, the diOerences do 

 not amount to much. In C. bartoni the depression of the carapace and the width 

 of the areola differ only in the degree of the development from the same character 

 in the burrowing species. C. limostis isihe most strongly markeil species, but should 

 not be compared with the other river-species of Pennsylvania, but with its nearest 

 relations in southern Indiana (C. indianensi.t Hay), but then again the difference 

 is small and consists only of quantitative changes in tiie same features. 



Thus the assumption of De Vries, that species have originated by sudden 

 leaps, does not find any support whatever in tlie conditions seen among the 

 crawfishes of Pennsylvania. On the contrary the close afllnity of most of them, 

 and the comparative insignificance of the specific characters, supports the view 



