SOMITES AND APPENDAGES. 145 
plates, of which one is attached to the inner side of the 
extremity of the protopodite, and is called the endopodite 
(en.p), while the other is fixed a little higher up to the 
outer side of that extremity, and is the exopodite (ex.p). 
The exopodite is shorter than the endopodite. The 
endopodite is broad and is undivided for about half its 
length, from the attached end; the other half is narrower 
and is divided into a number of small segments, which, 
however, are not united by definite articulations, but are 
merely marked off from one another by slight constric- 
tions of the exoskeleton. The exopodite has a similar 
structure, but its undivided portion is shorter and nar- 
rower. The edges of both the exopodite and the endo- 
podite are fringed with long sete. 
In the female crayfish, the appendages of this and of 
the fourth and third somites are larger than in the male 
(compare D and E, fig. 37). 
The fourth and fifth somites, with their appendages, 
may be described in the same terms as the third, and 
in the sixth there is no difficulty in recognising the 
corresponding parts of the somite; but the appendages 
(fig. 87, F), which constitute the lateral portions of 
the caudal fin, at first sight appear very different. In 
their size, no less than in their appearance, they depart 
widely from the appendages of the preceding somites. 
Nevertheless, each will be found to consist of a basal 
stalk, answering to the protopodite (ca.p), which how- 
ever is very broad and thick, and is not divided into two 
L 
