THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS 75 



to have no grounds for connecting fresh-water life with these peculiarities of 

 crayfish. The marine ancestors of crayfish may have already acquired some con- 

 nection of young and parent before leaving the sea and in fact the life in bays 

 and estuaries would be one in which the dangers of loss of young if set free 

 early and swept out to sea, would make an attachment to the parent especially 

 valuable! And, later, the main advance of crayfish ancestors having been pre- 

 sumably up rivers and across country from river to river, the advantage of hav- 

 ing the young not set free early when they might more easily drift down 

 stream or be devoured, but when they were large enough and able to crawl and 

 to hold to the bottom, would perhaps lead to a continuance and perfection of 

 family life. 



But while it is easy to speculate on the origin of the characters of cray- 

 fish on the assumption of utility and the working of natural selection, the con- 

 clusions are of doubtful value in our present relative ignorance of their actual 

 life. Moreover, the nature and the amount of differences in the hard parts and 

 in the larval history that distinguish one kind of crayfish from another are such 

 as to raise the question whether utility and natural selection have played any 

 part in their formation or in their perfection. All the specific and generic 

 characters of crayfish may be as useless as color differences, and they may have 

 suddenly arisen perfected as we see them, or they may have progressed in 

 certain lines for long periods of time independent of external agencies. We need 

 more evidence from observation and from breeding experiments before con- 

 cluding that such characters as the shape of stylets and annulus or of rostrum and 

 of spines, absence or presence of one gill filament more or less, or the behavior 

 of telson glands and the presence of feathered setae instead of simple spines, 

 have ever in any manner been connected with utility to the species or with the 

 survival or the extinction of individuals. Until the contrary is proven we may 

 regard these as the unmeaning by-products of unknown activities in the living 

 protoplasm. 



