Packakd] insects of THE POND AND STREAM. 139 



it is forced to rise for more. In tlie travels of Colymbetes, 

 a near all}'' 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. How useful it may be to the insect in 

 pusliing its way through any obstacle may be demonstrated 

 b}' holding it tightly between the fingers ; here even it man- 

 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 Avindows. 



Siebold says that Hydropliilus jnceus (Fig. 102, from 

 P'iguier), the largest of all the water beetles, and belonging 

 to a different gronp 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 Notoneda 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 oii its back) has a longitudinal ridge in the 

 middle ; a broad gutter between this ridge and the sharp 

 edge of the bod}' is bridged over from the head to tlie end 

 of the abdomen l)y a layer of dark, coarse, oblique hairs, 

 and a layer of less obliciue hairs arises on each side from tlie 

 middle of the ridge. These hairs thus form a false upper 

 deck. Tlie 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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