Chap. XII.] THE CRAYFISH. 237 



Fig. 74, A. represents diagrammatically the second maxilliped. 

 The third maxilliped is similar in principle, as is also the third 

 leg. The forceps and the first two legs have the dactylopodite 

 so disposed as to form with the propodite a chelate termination 

 to the limb, as shown in I. In the fourth leg the epipodite is 

 suppressed. B. is the first maxilliped in which, as in the maxillae, 

 the protopodite is very thin and flattened. In the second 

 maxillae the divisions 1 and 2 are cleft ; the endopodite is small, 

 and the epipodite either coalesces with the exopodite to form, or 

 is itself modified into, a long curved plate, the scaphognathite. 

 In the first maxilla both exopodite and epipodite are suppressed ; 

 the endopodite is small. The mandible (C.) is stout and strong, 

 being mainly protopodite, with a small-jointed palp, supposed 

 to be the endopodite. In the antenna (D.) the endopodite is 

 enormously produced, and the exopodite forms a flattened 

 squame. In the antennule (E.) the protopodite has three 

 joints; both endopodite and exopodite are elongated. In 

 the ophthalmite (F.) we appear to have all suppressed but the 

 protopodite. 



In the abdominal region the typical appendage is as in G. 

 The first two pairs of appendages in the male are specially modi- 

 fied, the endopodite of the first being so rolled upon itself as to 

 enclose an incomplete canal. The first abdominal appendage in 

 the female is very small, and sometimes wanting ; its exopodite 

 is suppressed. In the posterior pair of abdominal appendages 

 of both sexes we have much metamorphosis, the endopodite and 

 exopodite (H.) being flattened and expanded, so that the two 

 pairs, with the telson, form' the broad tail-fin. 



It will be noted that many of the appendages are jointed ; 

 whence a large division of invertebrates with such jo 

 are known as the Arthropoda (arthron, a joint; 

 The joints are such as to allow the successive segments of the 

 limb free play in one plane. The third leg, for example, is 

 so hinged at its connection with the thorax as to allow the 

 coxopodite to move backwards and forwards, but not up 

 and down. Referring to the other divisions by numbers, 

 we may note that the motion between 1 and 2 is up and 



