156 
HALF HOURS WITH INSECTS. [Packard. 
the body. By dexterous strokes, aided by a graceful but 
rapid bending of the body, it seeks the surface and inspires 
air through its thoracic respiratory tubes. In the same way 
it descends to the bottom. 
The Corethra larva alters the specific gravity of its body 
during the course of its wriggling, but as a pupa all this is 
changed. It now resembles the mosquito pupa, has exter¬ 
nal thoracic respiratory tubes and well developed tracheae; 
it loses its air bladders and swims by means of two terminal 
paddles like those of the mosquito. 
We now come to the water beetles and bugs, whose move¬ 
ments in the water are as graceful 
as they are awkward on land. 
Their whole organization, bodily 
and psychical, as thoroughly 
adapts them for the water as that 
of the seal or whale for the same 
element. They are the Amphibia 
of the insect w r orld. Born as 
sailors, they take to the water on 
being hatched and there remain 
through their lives, only leaving 
one pond to seek another, im¬ 
pelled by a restless love of change, 
Fig. 124 . 
n 
i 
Baetisca. 
which unconsciously to themselves results in good to their 
race, preventing too close in-and-in breeding and the conse¬ 
quent deterioration of the stock. Look at the body of the 
Dytiscus (Fig. 125), so perfectly adapted for its aquatic 
life. Remember that it is in reality a modified ground bee¬ 
tle, such as Harpalus, the mouth-parts much the same, and 
that the changes in form are mostly, if not wholly, such as 
adapt it to its aquatic life. The body is oval, both, ends 
alike, as in a boat, while the legs are perfect oars. The 
hind legs, instead of being broad and spiny towards the 
claws, as in the running ground beetles, taper to a point 
28 
