66 TWELFTH REPORT. 



TWO ABNORMALITIES IN THE CRAYP^ISH. 



LUCIE HARMON. 



Numerous instances of abnormalities in the crayfish have been reported 

 from time to time, and various causes for such growths have been dis- 

 cussed, but as yet no definite conclusions have been reached. The two 

 cases here described are presented with the hojDe that they may serve as 

 additional material for a future solution of the causes of abnormal 

 growth. 



The first case to be described is that of an aberrant limb on a male 

 Camhartis vir'iUs (Hogen). The s|>efimen was obtained from Nortli Jud- 

 son, Indiana. Though in other respects the animal is perfectly normal, 

 the third right walking leg has five projections from the protopodite. 

 The dactyl and index on the outer side of the leg are normal, but on 

 the inner side there are three additional claws, two not articulated 

 but about the size of normal claws; a third, lying between these two, 

 very small, slightly movable, and deeply set in a socket. The pair of 

 normal claws and the longest two of the abnormal claws have each one 

 row of serrated plates arranged along their approximating sides. The 

 tiny claAV bears two rows of serrated plates, facing those of the large 

 claws between which it lies. These are more pronounced on the inner 

 than on the outer side and are longest on the tip. The four large claws 

 bear horn-like tips, but this condition is not present in the tiny claw, 

 though the latter has a slight protulierance on its posterior surface 

 near the tip. On the anterior face of the distal third of the protopodite 

 there is a slight injury, and this is located on that side of the leg from 

 which the abnormal claws originate. 



From the mass of literature regarding abnormal crustacean appendages 

 I have selected the following citations as being most significant in their 

 bearing upon the present case. 



Nusbaum,^ who worked upon chelipeds of crayfish thinks that ab- 

 normalities are due to enlargements which often accompany regeneration 

 of broken parts. 



Margaret A. Reed,- who was one of Prof. Morgan's students, reflects, 

 in her investigations upon the hermit crab, the views which he held 

 at that time. She says: "If after the leg of the hermit crab has been 

 thrown otf at the breaking joint, the base is split lengthwise, so that 

 the nem'e is divided or cut in two, there often appear two new legs, 

 one connected with each end of the old nerve." 



Herrick^ describes eleven cases of abnormal appendages in the lobster, 

 but only two of these are on ambulatory legs, one a bifurcating dactyl, 

 the other a trimerous dactyl. He 'says, "'Defective or deformed claws, 

 the result of injury in different stages of repair, are met with every 



^Nusbaum, Josef, :07. Kleiner Beitraar zur atavistischen Regeneration der Scberen beim 

 Flusskrebse, Arch. f. Entw-mecb., Ed. 24, pp. 124-130. 



-Reed, Margaret A.. :04. Tbe Regeneration of tbe First Leg of the Crayfish. Arch. f. 

 Entw-mecb., Bd. 18, pp. 307-316, T. 17, 18. 



sHerrick, F. H., •06. The American Lobster. Bull. T^ S. F. C, Vol. 1.5, (1S95), pp. 

 1-252, Is. 1-54. 



