SECONDARY SEXUAL CHARACTERS OF CRAYFISHES. 235 



and northern Ohio. About 2 per cent, of all the males of Camba- 

 rus propinqims examined have been aberrant in this respect. In 

 Cambarus virilis the general occurrence of specimens with super- 

 numerary sexual characters is less but locally the proportion of 

 specimens abnormal in this respect mounts up to 33 per cent. 



If the cause or causes underlying the peculiar condition is to be 

 studied to advantage it would be in localities in which the 

 proportion of peculiarites was remarkably high. 



2. The manner in which specimens with supernumerary hooks 

 var\ 1 n MII the in >rmal seems to have a certain degree of o nn-tancy 

 in a gix-en >pccies. In Cambarus virilis, for example, the devi.i- 

 tii-n is always in the direction of the development of additional 

 hooks upon the second walking legs. In Cambunis f>rof>hiqnns, 

 on the other hand, the additional hooks may be developed upon 

 either tin- fourth or the second walking legs btit never upon both 

 the fourth and the second walking legs in tin- *ame .-pccimeii. 



3. I >e\ iaiion has thus far always been in the direction of in 

 than the normal number of copulatory hooks and not U-- than 

 normal. Thi> has held for all species examined \\hetlier t hex- 

 normally possess copulatory hooks upon the third and fourth 

 \\alking leg>, as in the case of Cambarus blamiiitgii at utu- and 

 Cambarus clarkii, or upon the third walking legs onl> as in all 

 >pe< ie> of the subgenus Faxonius and the subgenu> tturtonins. 



.}. It i- -digested that, in Cambarus propinquity >ince the 



nd, third and fourth walking legs are potential bearers of 



copulatory hooks a specimen may be found e\pre>>ing the 



extreme decree of deviation from the normal condition and 



bearing copulatory hooks upon all three of these \\alkinj; legs. 



