12 ANIMAL ACTIVITIES. 
at the same time and kept in aquaria. If possible 
collect a water-boatman. Fig. 72 shows this insect 
Fic. 13.—Caddis-fly Cases. 
as it appears while swimming and while flying. A 
powerful aquatic insect is the large water-beetle (Dity- 
cus Marginalis). Fig. 15 shows the young and Fig. 
Fic. 15.—Larva,of Dyticus. Fic. 16.—Larvaof Fic. 17.—Larva 
Whirligig Beetle. of a May-fly, 
73 shows the adult forms. The whirligig beetles seen 
in large numbers on the surface of fresh water have 
eyes adapted for seeing enemies in the air above and 
