12 



of a large basal joiut or pi()t()})Oflite bearinfr two similar 

 niany-joiuted rami (exopodite and eiidopodite). Each 

 joint of tliese bears long, plumose sette, 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 brauchise, 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 protopodite, bearing two stout rami (endopo- 

 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. Both rami bear long plumose setse in addition to the 

 spines, and are apparently 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 setDe. 



The Body-Wall axd 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 setie which it bears. It forms a complete 



