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protopodite, a small endopodite, and exopodite, and a large spoon- 
like epipodite, which serves a special purpose, and is termed the 
scophagnathite, or boat-like jaw. The next pair in advance is 
composed of the first maxillae, and each such maxilla is small 
and delicate, and consists of the same parts, except that the 
epipodite is rudimentary. In front again are the two man- 
dibles, and each mandible consists of a large expanded proto- 
podite (a true crushing jaw) to which is attached a very small 
jointed endopodite — here termed a jpaljp. The exopodite, as in 
the locomotive limbs, aborts. Between the two mandibles the 
mouth opens, and in front of it the sternal surface bends rather 
sharply upwards in what is termed the cephalic flexure,” in 
consequence of which the more anterior appendages are directed 
altogether forwards, and not downwards. The pair immediately 
in front of the bend is formed of the two long feelers (the 
antennce), and each antenna consists of a protopodite and a 
long filamentary, much segmented endopodite, to the outside of 
the base of which a rudimentary exopodite (like a small scale) 
is attached. The pair of appendages next in front is formed of 
the antennules, and each of these consists of a protopodite 
bearing both exopodite and endopodite, and these are both 
much segmented and pretty equally developed, in the latter 
respect returning to the type of the abdominal appendages or 
swimmerets. 
The most anterior pair of appendages of all (unless indeed 
they should turn out not to be true appendages) is composed of 
the two eye-stalks, each eye-stalk being a protopodite, elongated, 
and bearing an eye at its distal end. Besides the lateral 
appendages at the sides, the mouth is bounded anteriorly by a 
simple median piece (the labrum), and posteriorly by a bifur- 
cating process termed the metastoma. The pleura of the 
thorax, instead of being only slightly produced (as before 
described, in the abdomen), are very much prolonged down- 
wards, leaving a considerable spRce (the gill chamber) between 
the true body and the much bent- down pleura on each side of 
the former. 
We are now in a position to see how great differences in size, 
form, and function may exist between parts which are essen- 
tially and developmentally the same. The antennule, antenna, 
mandible, foot-jaw, walking-leg, and swimmeret are all diverse 
modifications of one common structure. We have here an 
excellent example of what is called serial homology.” 
Passing now to other points in the creature’s anatomy, we 
will begin with the mouth, the situation of which has been 
already described. This leads by a short gullet to a large and 
globular stomach, divided into an anterior cardiac ” part and a 
posterior pyloric ” portion. These parts are so named by 
