No. 484] 



ATTACHED YOUNG OF CRAYFISH 



271 



From consideration of the larval lif'(> \v(> come to the same 

 general conclusion as that generally drawn from study of adult 

 anatomy and geographical distribution, namely that ("amharus 

 is a more highly evolved form than Astaeus and that (\ ajjiiiis is 

 one of the higher, more specialized forms of the genus. 



As to the relative position of (\ clarki't and ('. <//'o(/rnr.s there is, 

 however, doubt and (liserej)en(y-. The aihilt characters seem to 

 leave no doubt that C. clarkii is nmcli tlie more primitive, h-ss 

 specialized and more like Astaeus of the two. But in the adjust- 

 ment of the larva to family life (\ dUxirnrs would seem to have 

 progressed less far tlian (\ clarkii, at least in the first stage C. 

 diogenes has more segments in its second antenna and in the second 

 stage more. sense seta- in the first antenna as well as more segments 

 in the second antenna. ( )n the other hand (\ clarkii would be 

 more primitive in liaviiig more seta- over the ear-])it and if in 

 nature the yotmg actually get loose from the mother in the second 

 stage they would be more like A>tacu-^. 



be paid to the first three larval stages as ai<ls in determining the 

 relative positions of the species and their j)robable derivation 

 from ancestral forms. 



From a thorough study of larvai of many species and from experi- 

 ments in cross breeding some idea might be got as to tlie nature 

 of the causes that seem to be leading some of the more evolved 

 crayfishes to develop further that association of parent and off- 

 spring which forms in the crayfish a simple stage in family life. 

 December 20th, 1906 



