42 THE UNIVERSITY SCIENCE BULLETIN. 
Rheumatobates, too, dips below for ostrocods, etc., which 
it scoops out of the water and holds aloft upon the upturned 
tip of the beak while the body of the little victim is being de- 
pleted of its nutritive material. Microvelia and Mesovelia 
depend upon their stylets also for holding prey, and the fore 
limbs are very slightly thickened. The Gerris, Velia and 
Trepobates have thickened femora and use the fore legs in 
holding prey. The Saldide and Ochteride have the front legs 
modified slightly. In some of the Saldids the fore tibia is 
armed with a few spines so directed as to be of slight service 
in grasping. The Gelastocorids have the fore limbs well modi- 
fied into grasping organs. The femora are thickened and 
margined with stout spurs. The tarsal claws are heavy and fit 
against the coxe firmly. (See pl. IX, fig. 1.) 
The Naucorid carries this plan still farther, the femora 
being greatly enlarged with the tibia and tarsus fitting snugly 
against it when flexed. In the Belostomatids the same arrange- 
ment is found, though not to the same extent. In the genus 
Lethocerus the femora are grooved for the reception of the 
tibie. 
The Notonectids furnish an illustration of still further use 
of the limbs in the manipulation of prey. These insects do 
not cling to supports, but poise back downward in the water, 
thus freeing not only the front pair, but the middle legs as 
well, for service in retaining captured victims. In the genus 
Notonecta the femora of both fore and middle legs are large 
and armed with short spurs and spines. The members of 
this group are fierce predators and attack other insects often 
larger than they. (See pl. XX, fig. 8.) On the other hand, 
it is interesting to examine the limbs of the Buenoa modified 
for retaining prey—but very different kind of prey. These 
insects dart, poise and swim submerged, gathering in the 
Entomostraca by the half dozen, and retaining them impris- 
oned in a curious crib formed by the long, spiny armature 
of the flexed limbs. (See pl. XXIV, fig. 4.) Here the femora 
are not greatly thickened, but long and fashioned with a 
series of projections that make for efficiency in preventing 
the escape of small organisms. Notonectz nymphs feed on 
ostracods, etc., but seldom retain more than two at one time, 
and are not in the same class with Buenoa when it comes to 
