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 bod}^ 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. 



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 



