6 AMPHIPODA. 



attached to the head ; they have some of the joints foli- 

 aceous. They overlap the preceding appendages of the 

 mouth, and act as a protecting operculum. In the Hy- 

 perina they are small, and do not overlap the whole of 

 the buccal apparatus. 



The two anterior pairs of legs (gnathopoda, h and z), 

 which in the Podophthalmata are reduced in size, and 

 employed as two additional pairs of foot-jaws or pedi- 

 palps, are here developed into arm-like legs, and are 

 attached to the two anterior segments of the body. 

 They are directed forwards, and generally formed upon 

 the same type, the posterior being the larger ; but to 

 this general rule there are several exceptions. The sixth 

 joint (or propodos, e) is generally enlarged into a hand 

 in both pairs, against the inferior margin of which the 

 seventh joint (or dactylos, 7) doubles back, as a finger 

 against the palm, and impinging against it, gives to the 

 organ a prehensile capability. Sometimes the fifth joint 

 (or carpus, 5), and also the fourth (or meros, 4), are infe- 

 riorly produced, so as to assist in prehension. These ap- 

 pendages seldom attain the form of the analogous chelae 

 in the higher orders ; QalUsoma, Chelura, and one or two 

 others, being the few exceptions to this very general law. 

 All the legs have the first joint * (or coxa, i) developed 

 into a large and squamiform plate, which covers a con- 

 siderable portion of the second joint, and protects the 

 branchial organs (figure *, i" and i'" in p. 2,), as well as 

 the ova and embryos while confined within the incuba- 

 tory pouch during the period of gestation. In the four 



* By preceding writers, the series of scale-like plates at the sides of the 

 body have been regarded as the homologues of the epimera of the thoracic 

 segments of the Insecta. Mr. Spence Bate, however, considers them as the 

 first joints of the legs, thus dilated for special purposes in the economy of the 

 animals, an opinion which has been accepted by Professors Huxley, Kinahan, 

 and others. (I. 0. W.) The reader will observe that we employ the term 

 joint for a portion of a limb, and articulation for the connecting hinge. 



