ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 503 
cant ones in C. monongalensis. 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 tendency 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, which 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 
ease of albinism has been observed in C. diogenes. 
The conclusions from the above observations are that in the Cambarus forms of 
Pennsy]vania 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 eases of hermaphroditism cannot 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 et 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 the propinquwus-section, where the three forms, two of which at least must be re- 
garded as species, are distinguished by such insignificant characters that it is impos- 
sible to talk of “leaps” or of ‘sudden changes.” The same is true of the differ- 
ences of C. carolinus, C. monongalensis, and C. diogenes, 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 differences do 
not amount to much. In C. bartowi the depression of the carapace and the width 
of the areola differ only in the degree of the development from the same characters 
in the burrowing species. C. /imosus is the most strongly marked species, but should 
not be compared with the other river-species of Pennsylvania, but with its nearest 
relations in southern Indiana (C. indianensis Hay), but then again the difference 
is small and consists only of quantitative changes in the same features. 
Thus the assumption of De Vries, that species have originated by sudden 
leaps, does not find any support whatever in the conditions seen among the 
crawfishes of Pennsylvania. On the contrary the close affinity of most of them, 
and the comparative insignificance of the specific characters, supports the view 
