72 ENTOMOLOGY. 



The thorax is also peculiar in being globular, the pro- 

 thorax is small and collar-like, while the mesothorax is very 

 large, and the metathorax very small. The wings are finely 

 net-veined, and the hinder pair are very small, sometimes 

 wanting. The abdomen is very long and slender, ending 

 in three long, jointed stylets, while in addition there are 

 in the males beneath the stylets two pairs of jointed claspers, 

 a feature peculiar to these insects. Moreover, as in the 

 Dermaptera, the genital openings of both sexes are double; 

 in all other insects there is but a single opening. 



But if the May-fly takes no food, it is quite otherwise 

 with the larva and pupa. Fig. 57, a, represents the larva or 

 nymph of Palingenia; its body is long and slender, with 

 long slender antenna?, while the jaws are very large, the 

 creature being voracious and feeding on other insects. 

 Along the sides of the hind body are either leaf-like or 

 bushy tracheary gills, and the body ends in long hairy 

 bristles. 



The larva? are said to live two or three years, residing in 

 burrows in the mud. under stones, or among grass and 

 weeds, where they may be taken with the water-net in great 

 abundance, and are beautiful objects for the aquarium. 

 Some of the group, if not all, differ from other insects in 

 moulting so many times; thus Chloeon casts its skin 

 twenty-one times before it assumes the imago state. In 

 another respect the May-flies are peculiar: after transform- 

 ing from the nymph, the winged insect, called the sub- 

 imago, takes a short flight, and then casts another skin 

 before assuming the final, imago, state. 



May-flies often appear in immense numbers, and falling 

 into the water become stranded in windrows along the 

 borders of lakes. The perfect insects should be preserved 

 in alcohol for study, and described when alive if possible, 

 as the body shrivels up and the colors fade when pinned. 



Family Ephemeridae. Characters of the order. Poiamanihus mar- 

 ginatum Zett. (Fig. 57), Palingenia biUneata Say (Fig. 57, a, nymph). 



