ASTACID^E. 17 



THE SEXUAL PECULIARITIES OF THE ASTACID^E. 



The sexual differences, aside from the genital parts, are often very 

 considerable. In the female the great claw is shorter, smaller, and not 

 so well developed. The sculpture and armature are less, the postabdo- 

 men mostly broader, and its legs stronger. Apparently the females 

 have, in many parts, retained the characters of the younger animals. 

 But sometimes there are females with a development not at all inferior, 

 or with one even superior, to that of the males. I am not certain 

 whether, as in the males, any dimorphism is to be found. 



Abnormal Females. — It is not impossible in this way to explain, and 

 thus indeed may be explained, many apparent anomalies in females. 

 In these females we find a tendency to a more masculine development, 

 as in the aforesaid males a tendency to a feminine development. Never- 

 theless, even the rich materials of some species now in my hands are 

 not rich enough to enable me to solve by anatomical examination this 

 interesting question. 



The Abdominal Legs of the Males. — The sexual parts of the Astacidse, 

 especially in the North American Cambarus, offer very good and con- 

 stant specific characters. The abdominal legs of the Astacida? possess a 

 short, transverse, inwardly situated basal article, and a longer doubled 

 flagellum, consisting of two approximated narrow bands of a more mem- 

 braneous consistency, flexible, and sprinkled with hairs on the outside. 

 In the males, the first and the second pair are partly transformed. The 

 second pair has the basal half of the inner flagellum corneous and thick- 

 ened, but the apical half retains the same membraneous shape as the 

 external flagellum and the flagellum of all the following legs. The 

 corneous basal half is dilated at the end and rolled from the inside out- 

 ward, forming a channel. The first pair of abdominal legs is even more 

 transformed. The articulation between the basal limb and the flagel- 

 lum is gone, and also the whole external flagellum, as well as the mem- 

 braneous apical part of the inner flagellum. The remains of the first 

 abdominal leg form a corneous limb, with the apical half dilated and 

 rolled from the outside inward, forming also a channel. This kind of 

 shape is most easily understood in the true Astacus from Europe and 

 from California. In the American species of Cambarus we find the 

 modifications and different exarations forming, as stated before, very 

 good specific characters. The dilated apical half is so closely rolled 

 together that the channel no longer exists, except very superficially, 

 and the closely rolled part is transformed into two approximate cor- 

 neous solid cylinders, united above, while below there is an apparent 

 suture, constituting the rest of the channel before described. The tip 

 in each of the two cylinders is not simply truncated, as in the European 

 and Californian Astacus, but transformed into more or less corneous 



3 



