176 MANUAL OF ZOOLOGY. 



rower, and tlie former is undivided (fi<j- 49, 2). The last 

 thoracic somite immediately in front of the abdomen carries 

 a pair of the walking, or ambulatory, legs, each consisting of 

 a short basal piece, or ' propodite,' and of a long jointed 

 * endopodite,' the ' exopodite ' not being developed. The next 

 thoracic segment carries another pair of ambulatory limbs, 

 quite similar to the last, except for the fact that the protopo- 

 dite bears a process which serves to keep the gills apart, and 

 is termed the ' epipodite.' The succeeding segment supports 

 a pair of limbs similar to the last in all respects, except that 

 its extremities, instead of being simply pointed, are converted 

 into nipping claws or ' chela?.' The next segment of the thorax 

 carries a pair of chelate limbs, just like the preceding, and the 

 next is furnished with appendages, which are essentially the 

 same in structure, but are much larger, constituting the great 

 claws. The next two segments of the thorax, and the segment 

 in front of these (by some looked upon as belonging to the 

 head, by others as- referable to the thorax) bear, each, a pair 

 of modified limbs, which are termed ' maxillipedes,' or ' foot- 

 jaws.' These are simply limbs with the ordinary structure of 

 protopodite, exopodite, endopodite, and epipodite, but modi- 

 fied to serve as instruments of mastication, the hindmost pair 

 being less altered than the two anterior pairs (Jig. 49, 3). 

 The next two somites carry appendages, which are in the form 

 of jaws, and are termed respectively the first and second pairs 

 of ' maxilla3.' Each consists of the parts afore-mentioned, but 

 the epipodite of the first pair of maxillae is rudimentary, whilst 

 that of the second pair is large, and is shaped like a spoon. 

 It is termed the ' scaphognathite,' and its function is to cause 

 a current of water to traverse the gill-chamber by constantly 

 baling water out of it. The next segment carries the biting 

 jaws, or ' mandibles ; ' each of which consists of a large proto- 

 podite, and a small endopodite, which is termed the ' palp, ' 

 whilst the exopodite is undeveloped. The aperture of the 

 mouth is situated between the bases of the mandibles, bounded 

 behind by a forked process, called the 'labium,' or 'metastoma,' 

 and in front by a single plate, called the ' labrum ' (upper lip) . 

 The next segment bears the long antenna?, or feelers, each 

 consisting of a short protopodite, and a long, jointed, and 

 segmented endopodite, with a very rudimentary exopodite. 

 In front of the great antennas are the next pair of appendages, 

 termed the ' antennules,' or smaller antennae, each composed 

 of a protopodite, and a segmented endopodite and exopodite, 

 which are nearly of equal size. Finally, attached to the first 

 segment of the head are the eyes, each of which is borne upon 

 an eye-stalk formed by the protopodite. The gill-chamber is 



