Packard.] INSECTS OE THE POND AND STREAM. 139 
it is forced to rise for more. In the travels of Colymbetes, 
a near ally of Dytiscus, around the jar in which we have 
watched its movements, it often makes a squeaking sound, 
which we have heard at night as often as by day. This noise 
can be readily produced artificially by rubbing the end of 
the abdomen against the elytra, or wing covers. In this 
beetle there are six pairs of abdominal spiracles, but the 
basal pair are nearly three times as large as the others, and 
into these most of the air probably enters. In handling this 
beetle one is apt to be pricked by the sternal spine, which 
extends back of the insertion of the hind legs and is as 
sharp as a needle. Plow useful it may be to the insect in 
pushing its way through any obstacle may be demonstrated 
by holding it tightly between the fingers ; here even it lhan- 
ages to push its way out and drop to the ground. All the 
water beetles fly about in the night, exchanging one pond 
for another, and they sometimes enter our windows. 
Siebold says that Hydrophilus piceus (Fig. 102, from 
Figuier), the largest of all the water beetles, and belonging 
to a different group from Dytiscus, when it breathes, pro¬ 
trudes only its antennae out of water, and, “bending them 
backwards, thus establishes a communication between the 
external air and that adhering to the under surface of the 
body.” 
In our Notonecta undulata (Fig. 103) the mode of taking 
aboard its supply of air before diving is most admirable. 
The deck of the boat, i.e., the under side of the body (for 
the insect swims on its back) has a longitudinal ridge in the 
middle; a broad gutter between this ridge and the sharp 
edge of the body is bridged over from the head to the end 
of the abdomen by a layer of dark, coarse, oblique hairs, 
and a layer of less oblique hairs arises on each side from the 
middle of the ridge. These hairs thus form a false upper 
deck. The creature rises to the surface, the end of the body 
projecting slightly out of water; the air passes up on each 
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