212 
IOWA ACADEMY OF SCIENCES. 
the water in which they live, and in this remain protected and 
from it extend themselves to obtain food. The food is for the 
most part apparently minute aquatic organisms, algae, etc. 
Their presence might be considered a means of clearing water 
of such matter did they not at times become so numerous as to 
prove an element of danger. 
Fig. 12. (CMronomus sp.) a, larva, dorsal view, h, side view, c, head and first seg- 
ments of body, d, terminal segments of body showing appendages, e, upper surface 
of head. /, lower surface of head, p, side. dorsal, i, ventral view of pupa. (Orig- 
inal, drawn by Miss King.) 
