318 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
On each side in the region of the coxae there are masses of dor so- 
ventral muscles. The chief muscles here, however, are those which 
originate on the dorsal and on the ventral walls and serve to move 
or fix the coxae. Many of these are long and pass inward to take 
their origin on the dorsal shield near the origin of the two strong 
bundles of mandibular muscles. 
In the male the lines on the dorsal shield indicate the place of 
origin of these muscles to the coxae. The scutum in the female is 
relatively very much smaller and absolutely somewhat smaller. As 
the female moves very little, and when gravid never from her place 
of attachment, there is need for less powerful muscles than in the 
case of the active male. 
There is also a system of longitudinal muscles chiefly along or 
near the dorsal side of the animal. The two heavy bundles which 
are inserted on the mandibles and originate in the center of the scutum 
belong to this group. At the point where these muscles originate, 
above the brain mass, they are flanked by other longitudinal muscle 
bundles which pass backward and are inserted on the body wall, 
back of the stigmata. 
The muscle of the beak gives the animal a means of maintaining 
a rigid hold on the host and is therefore the heaviest muscle in the 
body. It is possible that the flanking muscles aid these which set 
the mandibles by making more rigid the posterior edge of the scutum. 
Most of the muscles enumerated, by contraction might bring pres¬ 
sure to bear on the tracheae, decrease their containing power, and 
thus function for respiration as does the diaphragm in man. 
The dorso-ventral and longitudinal muscles are useful in the case 
of the female to decrease the size of the abdomen and thus to force 
eggs out of the expanded uterus at the time of oviposition. During 
egg-laying the lines on the abdomen become much deeper and more 
distinct. 
A few bundles of fibers separate from the dorso-ventral rows were 
spoken of as inserted on each side of the genital opening. These 
are inserted on the wall of the uterus where it is heaviest and most 
muscular. A good drawing of this system of fibers is shown by 
Pagenstecher (’61) in his pi. 2, fig. 6. Other fibers come from the 
ventral floor of the body cavity on both sides. The shell gland on 
each side seems to be twined about these uterine muscles to some 
extent. 
