SOMITES AND APPKNUAGES. 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 cxopodite iex.p). 

 The exopodite is shorter than the endopodite. The 

 endopodite is hroad and is undivided for ahout 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 consti'ic- 

 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 seta3. 



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. 37, 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, the}' depart 

 widely from the appendages of the preceding somites. 

 Nevertheless, each will be found to consist of a basal 

 stalk, answering to the protopodite {cx.p), which how- 

 ever is very broad and thick, and is not divided into two 



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