114 University of California Publications. [ ZooLocy 
In typical groups the abdomen proper consists of five seg- 
ments in the male, and always less than five in the female; fu- 
sions often reduce the number of segments to as few as one or 
two. The first segment of the abdomen in each sex bears the 
orifices of the sexual organs, and is called the genital segment; 
the last segment contains the opening of the alimentary canal, 
and is called the anal segment. The furca is a paired appendage, 
borne on the anal segment and carrying usually a fringe of six 
bristles of various lengths. The anterior portion of the head 
segment is known as the front, and terminates ventrally in the 
rostrum. The latter may consist of one or two strong, pointed 
projections, or of the same number of long, slender filaments. 
The appendages of the cephalic segments in order are, from 
front to rear: (1) The anterior antennae; (2) The posterior 
antennae; (3) The mandibles; (4) The mawillac; (5) The ante- 
rior maxillipeds (second maxillae); (6) The posterior maxilli- 
peds (maxillipeds). The thoracic segments bear the swimming 
feet (four pairs), and also a fifth pair of feet which usually are 
modified in both sexes, and at times are absent in the female. 
The cephalic appendages from 3 to 6, inclusive, are the mouth 
parts. All the appendages except the anterior antennae are 
typically biramous: each consists of a two-jointed basal part 
(basipodite), which bears the inner and outer rami (respectively 
endopodite and exopodite). Neither ramus is more than three- 
jointed, and in many forms the number of joints is reduced by 
fusions. 
The anterior antennae in the Gymnoplea consist of 25 joints, 
but this number may be reduced by fusion. The joints 
earry bristles and sense organs, or aesthetasks. The joints in 
an appendage, or a part of one, are numbered from the base 
to the tip. Among the Gymnoplea one of the anterior antennae 
of the male may be modified to form a grasping organ; this is 
usually on the right side, but both appendages may be so modi- 
fied. The grasping organ may be recognized by its want of 
symmetry. The joints on either side of the geniculation are 
often provided with teeth. In many of the Gymnoplea the fifth 
feet in the male form grasping organs; the fifth feet are always 
asymmetrical in the male, whether they form grasping organs. 
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