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- 
per in a they are small, and do not overlap the whole of 
the buccal apparatus. 
The two anterior pairs of legs (gnathopoda, h and *), 
which in the Podophthalmata are reduced in size, and 
employed as two additional pairs of foot-jaws or pedi- 
palps, are here developed into ann-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, 6 ) 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 ; Callisoma , Chelura , and one or tw r o 
others, being the few exceptions to this very general law. 
All the legs have the first joint # (or coxa, 1) developed 
into a large and squamiform plate, which covers a con- 
siderable portion of the second joint, and protects the 
branchial organs (figure *, 1" and T" 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, tlie series of scale-like plates at tlie 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. 
