ASTACID^. 21 



the sexual aperture is visible at llic base of the third set of legs. The 

 fust abtlouiinal seguieut is without auy appearauce of abdominal legs ; 

 iu all the other seguieuts the al)doiuiual logs are well developed, their 

 length being nearly two thirds of the breadth of the postal:)douieu, the 

 basal artiele being oblong, while the length of the doubled flagelhun is 

 a little greater. 



In the males the first segment has on each side a little knob, some- 

 what longer than broad, turning inward. In the interior the developing 

 leg is visible, and its articulation seems marked. This oval knob, with 

 rounded tip, is the beginning of the first pair of abdominal legs. I have 

 seen the same form of the first abdominal legs in the young of (7. Bar- 

 tonii, even 0.55 inches long. Tab. II. Figs, loo, 134. 



Second Form of the Mitks. — I have examined the further development 

 in Cumharus acuins. In the younger specimens, 1.7 inch long, the legs 

 are more developed, the basal third articulated. The shape of the legs 

 is nearly the same as in the full-grown animal, l^ut narrower, more 

 cm'ved, the tij) a little broader, the teeth more obtuse. In the older 

 specimens, 2.7 inches long, the legs are the same as in the full-grown 

 animal, which is over four inches long. Occasionally, both in younger 

 and in full-grown specimens, the articulation is partly gone, but its 

 remains are still visible on the upper margin; in some cases the 

 articulation has entirely disappeared. 



This form, which is always visible in the ver}^ young and in middle- 

 aged specimens, ordinarily with an articulation, I have described as the 

 second form of the male. 



First Form of the 31alcs. — In all species seen and examined by me, 



many old, full-grown males have the first pair of legs of a 2:»articular 



shape, analogous in a certain view to the form before described, and 



•always found in the young animals, but differing in the following 



particulars. 



The articulation is entirely gone ; the tip of the leg is more dis- 

 tinctly finished and not so membraneous ; the hooks are horny ; the 

 teeth or bifid ends longer and more se2)arated ; the hairyness, if any 

 exists, more profuse. I have figured these parts in nearly all the 

 species, and described them as the first form of the male. I think it is 

 well to observe that, in the second form of the males, they are always 

 developed in a manner visibly less complete than in the first form. 



The males of the second foi'm differ also in another way from those 

 of the first form. The hooks on the third article of the third, or in some 

 groups of the third and of the fourth, pair of legs are smaller and less 

 developed. The whole body has less size and Avidth, the sculpture is 

 not so well finished, while the claws are shorter, narrower, and more 

 like those of the female. 



A closer examination of the rich materials at the Museum shows that 



