306 ZOOLOGY 



resembling the dorsal part of the scaphognathite, but quite free 

 from the exopodite. 



In the second and third maxillipedes the two divisions of the 

 protopodito lose their expanded flat character; the enclopodite 

 becomes larger and larger, consisting of the definite five joints ; the 

 exopodite becomes relatively smaller ; and the epipodite takes the 

 form of a small oval plate bearing a gill. (For description of gills, 

 see 20). 



In the pincers and four walking -legs the exopodite is wanting ; 

 the epipodite with its gill is similar to that of the two hinder 

 maxillipedes (except in the fourth walking leg, which has none). 

 The main portion of the limb consists of the two joints of the proto- 

 podite and the five of the endopodite. 



In the pincers, and often in the first walking-leg, the basipodite 

 and ischiopodite are fused together or, more accurately, the cuticle 

 is continuously calcified over both, and no motion can occur at their 

 junction, which is recognizable by a slight surface-marking only. 



In the pincers and first two walking-legs the propodite has a 

 distal prolongation, as long as the dactylopodite, and the latter 

 bites against it, forming an excellent nipping mechanism. This is 

 called a chela, and these limbs are said to be chelate. It is a 

 curious thing that the process of the propodite is developed on the 

 postaxiaFside in the pincers and on the opposite side in the other two. 



The third and fourth walking-limbs are not chelate. 



8. Abdominal Appendages. The swimmerets consist each of a 

 two-jointed protopodite, and an exo- and an endo-podite which are 

 very similar and many- jointed. Most of them are rather larger 

 in the female (where they serve for the attachment of the eggs 

 between the times of laying and of hatching) than in the male. 



The first pair, however, is quite vestigial in the female ; whereas 

 in the male it is specially enlarged, the exopodite is absent, and 

 the endopodite is hard, unjointed, and grooved. The second in the 

 male is large, has a small exopodite, and the basal joint of its 

 endopodite resembles the appendage in front. These grooved 

 appendages serve to transmit the seminal fluid from the male genital 

 apertures to the ventral surface of the female. 



The last pair of abdominal appendages has small protopodites, 

 and broad flattened exo- and endopodites, the former of which alone 

 are two-jointed. 



9. Articulations and Tendons. It will now be well to get a clear 

 idea of the structure of the articulations between the various movable 

 sclerites that make up this skeleton. Any one of the articulations of 

 the walking-legs or pincers (fig. 151) will do to illustrate this. If 

 we examine such a one we find that the area of soft cuticle between 

 the two sclerites is divided into two by the approximation of the 

 sclerites to one another at two opposite points, where one has a 

 rounded peg-like projection which fits into a socket of the other. 



