PSEUDONEUROPTERA. 153 



so, as in Ephemera, Palinyenia, and Leptophlebia, one of the teeth extending in a 

 long, sharp point beyond the head ; most of them, however, feed on mud or minute 

 aquatic plants. The habits of the larval Ephemera? vary somewhat. Some prefer 

 running streams, others inhabit quiet basins or sluggish streams; in these situ- 

 ations they reside 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. It is generally agreed by authors, that in their preparatory 

 state they live for two or three years, though we doubt if most species live longer than 

 nine or ten months, hatching in summer and acquiring their wings the following 

 spring, before acquiring wings, so that the whole life of some Ephemeras may be 

 much longer than that of most insects. 



The number of moults, or changes of skin, is unusually great in these insects. The 

 larva of Heptagenia has been found by Vayssiere to shed its skin eight times before 

 leaving the water, i. e. there are nine stages of immaturity. The extreme in the num- 

 ber of stages is seen in Cloeon, which has been found by Lubbock to moult its skin 

 twenty-one times before assuming the imago state, or twenty times before it leaves the 

 water. 



Shortly after the winged insect casts its pupa-skin, it throws off a thin skin, or pel- 

 licle ; the insect, in this stage, is called the sub-imago, or pseudimago. The best 

 description of the process has been given by Westwood. When in the pupal stage 

 they crawl to the surface, where they cast off their pupa skin, appearing, at first sight, 

 to be fully developed, with the wings extended to their full size. " They then make 

 their way, flying with difficulty, to the shore, where they affix themselves to the trunks 

 of trees, stems of rushes, walls, or even persons standing upon the bank, when they 

 again cast off a very delicate pellicle, in which they had been entirely encased, and 

 which remains, unchanged in form, attached to the objects on which they had stationed 

 themselves. The skin, however, in which the wings had been enclosed, shrivels and 

 curls up into a mass, hanging down at the sides of the thorax. After this process, the 

 wings, disengaged from the outer covering, assume a brighter appearance, and the tails 

 grow to twice their previous length." 



Westwood invariably found that the casting off of this pellicle takes place during 

 the night. In some European species the operation of shedding the thin skin takes 

 place immediately after flight, and is so quickly performed that the whole operation is 

 over in three minutes, and the insect takes wing immediately after. Westwood adds, 

 that he has observed, in one instance at least, that the insect remained in the sub-imago 

 state upwards of twenty-four hours. 



We will now glance at the principal generic forms of these 

 interesting insects. In Ephemera there are three long caudal 

 filaments, of equal length. One of our commonest species, in 

 the northeastern States, is Ephemera (Leptophlebia^) cupida. 

 The largest species of the family belong to the genus Palin- 

 yenia, in which the middle caudal filament is shorter than the 

 others, or sometimes absent. It is common in our northern 

 lakes and streams late in the summer. 



The genus Eaetis has but two caudal threads: near this FIG. 224. - Potamanthus 



margmaius. 



comes the curious jBaetisca, already referred to ; then comes 



Potamanthus, which again has three caudal filaments. Fig. 224 represents P. mar- 



ginatus, which we have often captured in Labrador in July. It is also found in 



