152 
HALF HOURS WITH INSECTS. [Packard. 
was the so-called sub-imago ; after a few hours, if it had not 
been placed in the collecting bottle, it would have thrown 
off a thin pellicle, and then been sexually mature. It then 
lays its eggs in a round mass and dies. Some of the larvae 
live in burrows at the bottom of ponds, while others swim 
free. 
Coming, lastly, to the family of Dragon flies, we find 
among the larvae the most diverse means of respiration. In 
the young of Agrion (Fig. 119 ; a, respiratory leaf of larva) 
the body ends in three large leaves, through the middle of 
which runs a trachea which sends off a number of smaller 
branches. These larvae when quite small are beautiful ob- 
24 
