1976] Bow dan — Functional Anatomy of Gerris remigis 301 
on several long, broad, trochanteral apodemes. They effectively 
illustrate Hoyle’s (1975) statement that powerful muscles have 
many points of attachment. 
The reorientation of the gerrid leg about all three axes (Fig. 
1), produced by the rotation of the coxa and the angle of the tro- 
chanter, has altered the functions of muscles 46/47 and 50, al- 
though they are still antagonists. The main force developed by 
muscles 46 and 47 in Belostoma and Gelastocoris is a vertical 
one, and their function is to depress the trochanter and there- 
fore the extremities of the leg. In gerrids the main force developed 
is an anteriorly directed one which leads to a retraction of the 
leg (Fig. 6c). Muscle 50 in Belostoma and Gelastocoris raises 
the trochanter and the extremities of the leg. In Gerris, however, 
muscle 50 is the promotor of the leg (Fig. 6d). Muscles 40 and 
41 move the leg forward and backward, respectively, in Belostoma 
and Gelastocoris. In Gerris these muscles respectively raise 
and lower the leg. These changes are not only the result of the ro- 
tation of the leg axis, but also of a slightly different position of 
the muscles themselves. In Belostoma the trochantin is close 
to the anterior margin of the coxal rim, so muscle 40 inserts an- 
teriorly. In Gerris the trochantin is more posterior so that muscle 
40 and 41 are in the same anterior/ posterior position. Their 
antagonistic action is therefore across the anterior/ posterior 
axis of the coxa. In Belostoma their antagonistic action is across 
a more mediolateral axis (Fig. 8). 
L 
Figure 8: Diagrammatic representation of the insertions of muscles 40 and 
41 in a) Be /os tome b) Gerris. 
c r coxal rim 
