402 SYNOPTIC COLLECTION. 



young Plathemis, it may be a larva or a pupa (PI. 971, fig. 

 2), looks extremely innocent until a little crustacean or 

 insect passes by, then suddenly the mask is darted out, 

 as seen in No. 972, also PI. 971. fig. 2, and the prey is 

 secured. The legs of both larva and pupa are extremely 

 long. The rudiments of wings appear after the third or 

 fourth moult 1 and with their development the segments 

 of the thorax become greatly modified. 



The larval and pupal Plathemis breathes by tracheal 

 gills situated in the rectum at the posterior end of the 

 body. These gills are in the form of lamellae (fig. 3, 

 Plathemis vulgate} which are richly supplied with tracheae 

 (fig. 3). Instead of having three caudal gills at the end 

 of the abdomen, like the young Calopteryx and Agrion, 

 Plathemis has three chitinous valves (PI. 971, figs. 2,5; 

 No. 972). When these open, water fills the rectum and 

 the tracheal gills rob it of its air ; then it is thrown out 

 with such force as to send the insect swiftly forward. In 

 this way the water serves the double purpose of locomo- 

 tion and respiration. 



The pupal life lasts eight or ten months and duriiag this 

 time several moults take place. PI. 971, fig. 4, is a side 

 view of the last pupal skin shed by a male Plathemis tri- 

 maculata De Geer, and fig. 5 is a dorsal view of the pupal 

 skin (No. 973) shed by a female of the same species. 

 The former was drawn from a dry specimen, the latter 

 from No. 973, which had then been in alcohol a short 

 time. Both figures show the four tracheal threads that 

 extended from the inner side of the pupa skin to the 

 emerging dragon-fly, and which were shed with the skin 

 when the dragon-fly escaped. 



The adult Plathemis trimaculata De Geer (No. 974, $ ; 

 No. 975, 9 ; PI. 976, dissection of 9 ), retains the primi- 

 tive character of the ten distinct abdominal segments, but 

 various remarkable modifications have taken place in the 



1 Quoted from Poletaiew by Calvert, loc. cit., p. 197. 



