SECONDARY SEXUAL CHARACTERS OF CRAYFISHES. 



377 



FREQUENCY OF OCCURRENCE AND DISTRIBUTION. 

 The three specimens described here were the only ones taken 

 among approximately 3,600 males of Cambarus propinqnus. The 

 condition may, therefore, be considered rare. 



FIG. 4. Diagram illustrating three full pairs of copulatory hooks as they occur 

 upon the second, third and fourth walking legs of specimen No. 3. 



All three specimens were taken in a single section of one stream 

 (Pike River near Racine, Wisconsin) and constituted about 

 three per cent, of the males of the entire catch. Thirty-six 

 other streams and rivers examined contained no aberrant speci- 

 mens of this type. 



Male specimens with one pair of supernumerary hooks are 

 sometimes fairly abundant, in some localities representing as 

 high a proportion as seven or eight per cent, of all the males. 

 In Pike River, however, where the three specimens with two 

 supernumerary pairs of hooks were taken, fifteen per cent of the 

 males had one supernumerary pair of hooks, some of them 

 bearing the extra hooks upon the second and others upon the 

 fourth walking legs. 



DISCUSSION. 



Some direct and considerable' indirect evidence has been 

 accumulated indicating that in female crayfishes with male 

 secondary sexual characters the condition is inherited and should 

 be considered a germinal mutation. It is significant in this 

 connection that all three specimens of the males with two pairs of 

 supernumerary hooks should come from the same locality. It is 

 also suggestive that in this locality there should also occur by far 

 the largest proportion of males with one supernumerary pair of 



