HOW TO KNOW THE IMMATURE INSECTS 



4a. Front of head with 2 tubercles; mandibles curved outwards at tips; 

 r-^tennae with long cilia. Fig. 133 Family EPHEMERIDAE 



The naiads live in muddy bottoms or muddy water. 

 The body is elongate and more or less cylindrical. 

 The mandibles are long and tusk-like. The caudal 

 filaments are IcJbg and almost equal in length. 



Fig. 133. Hexo- 

 genio bilineota 



Say. 



4b. Not so. . . . 



5a. Abdomen with 6 pairs of gills; median caudal filament shorter than 

 the lateral ones. Fig. 134 Family PALINGENIIDAE 



The mandibles are large and protruding. The 

 median caudal filament is shorter than the lateral 

 ones. They live in Europe and Asia. 



Fig., 134. Polin- 

 genio sp. 



5b. Abdomen with 7 pairs of gills; median caudal 

 filament as long as« or longer than the lateral 

 ones. 

 Fig. 135 FamUy POLYMITARCIDAE 



The naiads sometimes dig into mud. The mand- 

 ibles are long and tusk-like. The caudal filaments 

 are equal in length. 



Fig, 135. Compsurus sp. 



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