12 



of a large basal joint or proioporlite beariii"' two similar 

 mauy-joiuted rami (exopodite and endopndite). Eacli 

 joint of these bears long, plumose sctpe, and the protopo- 

 dite bears a single long spine. These are the swimming 

 legs, and they keep up a constant current of water over 

 the branchipe, for they move rhythmically backwards and 

 forwards even while the animal is resting". 



The uropods (PI. II., uro. 1, 2, 3) are composed of a 

 basal joint or jn'otopodite, bearing two stout rami (endopu- 

 dite and exopodite) which are armed with two strong 

 spines on the upper margin, and two at the tip. The 

 protopodite of the first uropod is longer than that of the 

 second, so that the extreme tip of the former extends 

 about as far backwards as that of the latter (PI. II.). In 

 both hrst and second uropods the upper margin of the 

 protopodite bears two strong spines. The last uropod 

 (PI. I., fig. 14) has a short, thick protopodite, bearing two 

 rami, of which the endopodite is shorter than the exopo- 

 dite. lioth rami bear long plumose setse in addition to the 

 spines, and are apjDarently divided into many joints ; this 

 is not really the case, though they bear numerous circular 

 ridges. The inner ramus bears only one spine, near its 

 base. In G. locusta the last uropod is not so large as in 

 G. pulex, and does not bear plumose setse. 



The Bodv-Wall and Body- Cavity. 



The body-wall consist of (1) the calcified chitinous 

 cuticle or exoskeleton, (2) the hypodermis, (3) connective 

 tissue, which is mostly adipose. The chitinous cuticle is 

 continuous with the chitinous lining of fore and hind- 

 gut, and is cast at intervals, carrying with it these exten- 

 sions as well as the numerous spines and variously- 

 formed setai which it bears. It forms a complete 



