210 CALIFORNIA ACADEMY OF SCIENCES. 



The muscles surrounding the tubular structures are 

 also very complex, as has been shown. The plate to 

 which the ventral ends of the transverse fibers are 

 attached arises from the body-wall between the sterna 

 of the eighth and ninth segments of the abdomen (plate 

 XV, figs. 2 and 4, p). The proximal end of this plate is 

 non-chitinized but farther forward it becomes darker. 

 It ends in the ventral part of the groove formed by the 

 recurved ends of the first and second tubes. Its lateral 

 edges curve somewhat dorsally. The muscles are sur- 

 rounded by a very thin, delicate membrane (plate xv, 

 fig. 2, m) which along the median dorsal line sends a 

 fold downward a short distance to which the upper ends 

 of the transverse muscles are attached. In the middle 

 the muscles are seven or eight fibers deep but the num- 

 ber lessens toward each end. They curve laterally 

 around the tubes and each layer is attached to the 

 ventral plate internal to the layer just outside it. 



The longitudinal muscles, as stated, form a conical 

 mass of fibers converging upon the anterior end of the 

 rod, from which a few run forward to the sternum of 

 the metathorax. There are a few transverse muscles 

 within the others, especially close around the contained 

 tube (plate xv, figs. 2 and 5, Im). It is rather difficult 

 to determine how the longitudinal muscles are attached 

 posteriorly. It appears clear, however, that they are 

 not attached to any of the tubes but to the ventral 

 plate, and in the following manner: The anterior end 

 of the plate curves laterally very much upward around 

 the outermost tube. The upper lateral and dorsal fibers 

 posteriorly, in front of the recurved anterior ends of 

 the first and second tubes, curve downward and inward, 

 crossing each other in the middle line. They then 

 turn backward, passing over the rim of the tubes, and 



