6S4 



Form II. Since that time, in taxonomic work, a complete description 

 has always covered hoth forms of the male. 



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

 have been well described by Hagen^and Faxon^. 



The differences affect more especially those structures directly 

 concerned in the act of coition — the first pair of abdominal appen- 

 dages and the hooks on the ischiopodite of the third, or in some species, 

 of the third and fourth pairs of legs. In the second-form, the hooks are 

 much smaller than in the first-form and probably are incapable of per- 

 forming their function of attaching the male to the female during the 

 act of coition. The first abdominal appendages in the second- form have 

 almost the structure seen in the young males of the species. In the 

 first-form the articulation at the base is gone and the terminal hooks 

 are more widely separated and horny. In those species in which the 

 tip is bifid, the second-form appendage is divided but a very short dis- 

 tance and the ends are blunt, while in the first-form they are distinctly 

 separate for about half the length of the appendage and are slender 

 and horny. In the general form of the body the second-form approa- 

 ches that of the female; the sculpture of the whole body is less pro- 

 nounced and the chelae are seen to be decidedly more slender and 

 weaker than in the first-form. After a certain size has been reached 

 — all young specimens being second-form — no relation existe be- 

 tween the form and the size of the individual, the second-form speci- 

 mens being large and the first- form small or vice versa. 



Dr. H a gen made an anatomical examination ^ of first and second- 

 form males of C. acutus Girard, C. virilis Hagen and C. Bartonii Fa- 

 bricius. His observations were made from a very limited number of 

 specimens — probably only two from each species — and no note was 

 made of the time of year the material was taken, a condition the signi- 

 ficance of which he seems to have entirely overlooked. His observa- 

 tions were that the testis was decidedly larger in the first than in the 

 second-form. Hag en's idea was, that in the older males of the second- 

 form the sexual organs had failed to develop, and are consequently 

 n on-functional. 



The size of the arthropod testis, of course, depends largely upon 

 the condition of the sexual elements — being, for instance, larger 

 when the sperm cells are in the spermatocyte stages than when the 



* Hagen, loc. cit. 



5 Faxon, loc. cit. also: A Revision of the Astacidae, Part I. Mem. Mus. Comp. 

 Zool. Vol. X. No. 4. 1885. 



6 Hagen, loc. cit. p. 22— 24. 



