Piihistoiic Lake DwciUni/s of Sivitzcrlaud. 325 



until the first or second moult, as previous to this they breathe 

 cutaneously. 



It must be clearly understood that these organs are not 

 strictly branchia3, such as exist in the Crustacea, and in which 

 venous blood circulates, but tracheo-branchiaj, the air contained 

 in the water being absorbed through their substance, and taken 

 by the numerous trachea; radiating through them. 



Another form of gill is that of the lai'vge called caddis-worms, 

 in which rows of short isolated threads extend along the body. 

 Sidlis, the common little black-veined fly found by streams, 

 supplies another form of larval branchia3. Here seven pairs of 

 fine jointed tapering arms of some length project laterally, down 

 which the tracheae with their numerous little branches may 

 easily be detected. "When alarmed the creature directs them 

 slightly upward, and they appear comparatively rigid ; they are 

 equally useful for swimming backwards or forwards. 



Lastly, there is the enlarged rectum found in the LibeUula, 

 with its ridges and rows of short leafy processes. In this case, 

 as in the others, the same structure serves for locomotion and 

 respiration. By the muscular contraction of the cavity the 

 eft'ete water is driven out, and, when suddenly exerted, propels 

 the insect a considerable distance. 



Thus we see that the methods of respiration are very varied 

 and very instructive. In all cases the method adopted is the 

 one best adapted to the requirements of the individual. I do 

 not profess to have shown you more than a passing glimpse of 

 this aspect of insect life, and have selected those examples I have 

 met with and are most familiar rather than those which are 

 most curious or uncommon. 



94. — Notes on the Prehistoric Lake Dwellings of 

 Switzerland. 



By Edward Lovett. 



(Read April 8th, 1891.) 



The Lake Dwellings of Switzerland have attracted much 

 attention amongst ethnologists, owing partly to the great number 

 of relics found in the lake deposits, and also to the very great 

 interest that surrounds the remarkable people who lived during 

 that early period. The name of Keller stands pre-eminent 

 as an authority upon the subject, but numerous writers have 

 contributed to the bibliography of this very absorbing topic. 



