THE DIMORPHISM OF CAMBARUS, I. 



BY J. ARTHUR HARRIS. 



The existence of two markedly different forms of males in the 

 genus Camharus has long been known. The fact was first noticed 

 by Louis Agassiz and Henry James Clark,^ and communicated'^ by 

 the former to Dr. Hermann A. Hagen, who verified the observation 

 for all the species of Camharus, of which he had opportunity of ex- 

 amining a large number of specimens.^ Doctor Hagen, in his mono- 

 graph, whenever material was available, described both forms of 

 males, designating them as form I and form II. Since that time, 

 in taxonomic work, a complete description has always covered both 

 forms of the male ; a fact of no small importance, since the discrep- 

 ancies in the descriptions of some of the earlier writers may be due 

 to the fact that the presence of two forms of males in each species 

 had not yet been recognized. 



The external differences between the first- and second-form males 

 have been well described by Hagen* and Faxon.'' 



The differences may here be just as well stated in Doctor Faxon's 

 words :^ 



" The differences between the two forms affect more especially the first pair 

 of abdominal appendages, organs concerned in the act of coition, but also extend 

 to the general form and sculpture of the body. In one form [ unhappily called by 

 Doctor Hagen the 'second-form' ] the first pair of abdominal appendages have a 

 structure nearly like that seen in all young males. The hook on the third joint 

 of the third [in some species, of the third and fourth] pair of legs is small, and 

 in the sculpture of the shell and shape of the claws this form approaches the 

 female. In the other form [Hagen's 'first-form'], the articulations near the 

 base of the first pair of abdominal appendages are gone and the whole member is 

 much more highly specialized, the terminal hooks being horny, more widely sepa- 

 rated, and in every way more highly developed; in those species with bifid tips 

 to these appendages, the branches are longer, slender, more widely separated, and 

 stiffer; the hooks on the thoracic legs are longer and more perfectly finished, 

 the sculpture of the whole body is more pronounced, and the claws are longer 

 and more powerful. No intermediate conditions are found, and there is no rela- 

 tion between these forms and the size of the individual, the 'second form' being 

 large and the ' first form' small, or vice versa.'''' 



1. See Faxon (Walter), "On the so-called Dimorphism in the Genus Cdmbarus," Amer. 

 Jour. Sci., vol. XXVII, pp. 42-44. 



2. See Hagen (Hermann A.), "Monograph of the North American Astacidw," 111. Cat. 

 Mus. Comp. Zool., Harvard Coll. 1870. 



3. Hagen, loc. cit., p. 24. 



4. Hagen, loc. cit. 



.">. Faxon, loc. cit. Also, "A Revision of the Astacidee," pt. I, Mem. Mus. Comp. Zool., vol. 

 X, No. 4. 1885. 



6. Faxon, " On so-called Dimorphism," etc. 



[49]-K.D.Qr.-A x 2-April, '01. 



