330 THE RIVER-SIDE NATURALIST. 



in a district enables the climate of other water in that 

 neighbourhood to be ascertained readily by comparison 

 with it. If the water of a given site exhibits marked 

 differences in temperature from the standard of the neigh- 

 bourhood according to the season or time of day, its 

 climate is extreme, and the site cannot be inhabited by 

 species which require relatively cold water." Sir John 

 Lubbock states that during the first few days after birth 

 the young cast their skins several times, the intervals 

 between the moultings increasing by degrees. Adolescence 

 is evidenced by the advancement of the reproductive organs 

 internally, and externally by the growth of rudimentary 

 wings from the hind-quarters of the proper segment. The 

 forceps of the male also begin to bud forth, and in their 

 general form most nymphs nearly resemble the adult. Mr. 

 Eaton prefers the term nymph to designate all the sub- 

 aqueous stages in the early life of these insects, instead of 

 that of larva or pupa, which, in earlier authors, denoted 

 respectively the wingless and wing-budding conditions. 



He says : " May-fly nymphs mostly feed upon either 

 mud or minute aquatic vegetation, such as cover stones, 

 and the larger plants ; but (judging by their mandibles and 

 maxillae) some must be predacious. Many of them live in 

 concealment in the banks 'or under stones in the bed of 



streams, rivers, and lakes ; 

 others ramble openly among 

 water-weeds, and swim with 

 celerity. Certain genera are 

 restricted exclusively to large 

 rivers ; and one of these (Palin- 

 genid) is said to remain a nymph 

 for three years." 

 PUPA (NYMPH) OF EPHEMERA How long the nymph of our 



VULGATA (Westwood). Mayfly proper (Ephemera vulgata 



or danicd) remains in the nymph state is not yet thoroughly 

 ascertained. It often lives in the mud, and is found either 

 close to the surface or deeper down, according to the con- 

 dition of the atmosphere. 1 

 1 The larvae are often found in gravelly shallows close to the surface 



