I AQUATIC BEETLES 95 



of small slits. On microscopic examination these slits 

 were found to penetrate the epidermis of the roots, and 

 to lead to the small irregular air-spaces, which occupy 

 a considerable part of the interior of the roots. Some- 

 thing of this had been previously observed by Siebold, 

 who in 1859 described the larv^a as biting a hole in 

 the roots of Sparganium, passing the end of the 

 abdomen into it, pressing the spiracles by the help of 

 the curved spines close against the hole, and so draw- 

 ing the contained air into its body. Schmidt-Schwedt 

 believes that the pair of openings are made not by 

 the mouth but by the spines, and that the air is 

 drawn in by internal channels running along them.^ 



Aquatic Insects often find it a matter of some 

 difficulty to procure a sufficient supply of air, and 

 many ingenious contrivances appear as practical so- 

 lutions of the problem. None perhaps are quite so 

 remarkable as the present one. That the Donacia- 

 larva should have found out the air-reservoirs of sub- 

 merged roots, and possess special organs for tapping 

 them, is surely one of the curiosities of adaptation. 



The pupal cocoon is a close-woven, oval capsule, 

 attached to the same roots as those upon which the 

 larva feed. On the attached side the wall of the cocoon 

 is deficient, and a good-sized hole, previously closed 

 by the root itself, appears when the cocoon is torn 

 away. A number of small holes, penetrating into the 



1 Dewitz {Berl Entom. Zeits., Bd. XXXII. p. 5, 1888) be- 

 lieves that in Ha;monia, and presumably in Donacia also, the 

 spiracles serve for the admission of air to the body, as Siebold 

 maintained. Schmidt-Schwedt has {B.E.Z., 1S89) reaffirmed 

 his oritrinal statement. 



