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 Saldidae and Ochteridse 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 coxse firmly. (See pi. 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 

 tibise. 



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 pi. 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 pi. 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. Notonectse 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 



