664 LAuRA FLORENCE 
In segment 2 the four lateral strands frequently appear as three, because 
the two outermost fuse almost immediately after leaving their attachment 
between segments 2 and 3. At their proximal end these lateral strands are 
attached to the lateral body wall a short distance cephalad of the anterior 
border of the pleurite of segment 3, and at their distal end, when looked 
at from their ventral aspect, the innermost strand and a part of the 
next innermost are seen to underlie the three outermost of the central 
strands. The dorsal and ventral muscle plates are composed of segmental 
muscles in which the attachment between those of the successive seg- 
ments has become stronger than their attachment to the intersegmental 
folds of the body wall, so that the dorsal and ventral muscles can be 
dissected off as entire muscle plates. 
While the two sexes bear a close resemblance in the longitudinal muscu- 
lature of the abdomen, they show a marked contrast in the dorso-ventral 
musculature. In the male the digestive and reproductive organs occupy 
only the center of the abdomen, but in the female the ovaries occupy 
most of the lateral regions as well. In the male there is a powerful dorso- 
ventral musculature, which not only assists in respiration but plays an 
important part in the act of copulation. That part of each of segments) 
2 to 8 between the alimentary canal and the lateral body wall is filled’ 
with stout blocks of muscle, definite in number and arrangement for each 
segment (Plate LIX, 5). In segment 2 there are two blocks of muscle,| 
in segments 3 and 4 eight blocks, in segments 5, 6, and 7 nine blocks, 
and in segment 8 eight blocks. The tracheae from the stigmata to the) 
lateral trunk pass between these blocks of muscle, and between the muscle 
and the lateral body wall lie numerous fat cells. In segment 9, where) 
the muscles controlling a part of the copulatory apparatus originate, 
there are no dorso-ventral blocks of muscle. 4 
In the female there is a deep lateral indentation between the successive 
segments from 3 to 8, that between segments 6 and 7 being somewhat 
deeper than the others. Internally these indentations have the appearance 
of pillars or sections of the cuticula which divide the lateral parts of the 
successive segments into a series of small chambers. At the end of each 
cuticular pillar two bands of muscle are attached to the dorsal and ventral 
walls of the abdomen, and these curve close to the centrad wall of the) 
pillar. In segments 4, 5, 6, 7, and 8, in the anterior half of the segment 
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