March, 1913-] LenG : AqUATIC COLEOPTERA. 35 



series external to the first and capable of absorbing and holding the 

 aerated water from which an attenuated layer of air is supplied to the 

 space enclosed by the first series of curved hairs. Such hairs are 

 found in Elmidae, in Hccnionia, and in all the snout beetles like Tany- 

 sphyrus that live on aquatic plants and live habitually beneath the 

 surface of the water. Experimentally Brocher found Elmidse capable 

 of maintaining life for at least eight weeks in aerated water, but 

 dying soon in water deprived of air. Hccnionia was found to live 

 about three weeks deprived of air and indefinitely when kept sub- 

 merged but in communication with aquatic plants. Such beetles must 

 therefore be regarded as even more completely aquatic than those 

 commonly called water beetles. 



The interesting observations of Brocher are barely sketched in 

 these remarks, details of the respiration of many different aquatic 

 insects may be found in his papers published in the Annales de Biol- 

 ogic Lacustre, Vols. 4 and 5, 1909 to 191 1, with copious illustration 

 and with the strongest internal evidence of conscientious work. 



Early Stages. 



Special emphasis has so far been laid upon the imago stage. The 

 importance of the larval stage in which presumably the creatures pass 

 the greater part of their lives, feeding, growing and actively perform- 

 ing all their functions except reproduction, must be admitted; but un- 

 fortunately little beyond the most general information is available, 

 for since the days of Schaupp few hereabouts except Joutel have taken 

 any interest in rearing Coleoptera. The work thus far done on Amer- 

 ican species has been indexed by Beutenmuller, but the work of Euro- 

 pean authors is our main reliance and from it in part the following 

 remarks have been compiled: 



The larvae of Haliplidae, Dytiscid?e, Hydrophilidse, Gyrinidse and 

 Parnidae are purely aquatic, living wholly in the water, but not 

 swimming. The eggs are frequently laid upon plants out of the water, 

 sometimes within a silken enclosure, that of the Hydrophilidas being 

 provided with a curious prolongation as if the quantity of silk had been 

 excessive and twisted into a pointed appendage. The larvae of Par- 

 nidae and ElmidcC are attached to stones, etc., by lateral expansions 

 of the segments, and in the case of Dryops and Psephemis become 

 almost circular in outline, and so nearly resemble Crustacea that 



