150 
HALF HOURS WITH INSECTS. [Packard. 
Fig. 114. 
dalus (Fig. 114), which transforms into the large net-veined 
insect (Fig. 115) so formidable in appearance, and yet so 
harmless. A singular chapter in biology would be the life 
of this insect. The gigantic carnivorous larva, with its 
large head and enor¬ 
mous jaws, is provided 
with eight pairs of long, 
rather stiff, respiratory 
filaments. Dr. Hagen 
has called attention to 
the spiracles of this crea¬ 
ture, which are not usu¬ 
ally present with tracheal 
gills, and to the reason 
for their existence. It 
seems that like the Euro¬ 
pean Sialis (Fig. 116, 
larva and pupa) it lives 
some weeks out of water 
before its transformation 
into the pupa, which 
rests in an earthen co¬ 
coon in the banks of 
streams above water. 
The eggs (Fig. 114, a) 
are very large, and are 
deposited in a squarish 
mass on the stems of 
water plants. 
There is no more beau¬ 
tiful object for low powers of the microscope than the larval 
May fly (Fig. 117). The body is so transparent that the 
movements of the heart, the play of its valves, the circula¬ 
tion of the blood, the distribution of the trachem, the diges¬ 
tive canal and its movements, as well ds the action of the 
22 
Corydalus larva and eggs. 
