12 EEV. A. E. EATON ON RECENT EPIIEMEEIDiE OE MAYFLIES, 



planted in the pans, because the sap exuding from its broken stems appears to be 

 poisonous to these animals. 



The Young of the Ephemerid^. 



The term "nymph" is employed in this work to designate all the subaqueous stages 

 in the development of the young after it is hatched. The old-fashioned usage of " larva " 

 and " pupa," borrowed from the terminology of other Orders to denote respectively the 

 wingless and wing-budding grades of the nymph, seem scarcely worth retention ; for they 

 do not indicate precisely any definite epochs of particular importance in the life-history 

 of these animals. Nymphs are young which lead an active life, quitting the egg at a 

 tolerably advanced stage of morphological development, and having the mouth-parts 

 formed after the same main type of construction as those of the adult insect. 



Mayfly nymphs mostly feed upon either mud or minute aqviatic vegetation, such as 

 covers stones and the larger plants ; but (judging by tlieir mandibles and maxilla?) 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 amongst water-weeds and 

 swim with celerity. Certain genera are restricted exclusively to large rivers ; and one of 

 these {Palingenia) is said to remain a nymph three years. Gloeon {teste Sir John 

 Lubbock) moults twenty-three times, and is probably bred much more expeditiously than 

 Palingenia ; it is one of the genera found in streams, ditches, and ponds, or the shallow 

 parts of lakes. 



Besides the influence of flood and drought, or constancy of supply, the climate of the 

 water is largely concerned in determining the fitness or unsuitability of a particular site 

 for particiflar kinds of Ephemeridae. A knowledge of the water-climate needed by a 

 species renders intelligible the limitations of its geographical and local distribution. 

 The temperature of the ordinary land-springs in a district enables the climate of other 

 water iu that neighbourhood to be ascertained readily by comparison with it. If the 

 water of a given site exhibits marked difi'erences in temperature from the standard of the 

 neighbourhood, according to the season or the time of day, its climate is extreme, and 

 the site cannot be inhabited by species which require relatively cold water. 



The newly hatched nymphs are destitute of any visible muscular, nervous, circulatory, 

 or reproductive system ; their alimentary canal is incomplete ; and, being too small to 

 requii-e sjiecial breathing-apparatus, they respire through the integument at large. The 

 abdomen is 9-jointed, and the anteunaj and caudal seta^ have likewise fewer articulations, 

 and are less hairy than those of more advanced nymphs. Pohjmitarcys possesses the 

 third caudal seta even before it is hatched ; but Clocon is born without any trace of 

 it, and developes it gradually at a later period (Joly and Lubbock). 



During the first few days after their birth the young cast their skin several times, the 

 intervals between the moultings lengthening by degrees (Lubbock). Blood-globules and 

 rudiments of the tracheal branchitc begin to appear simultaneously when the insect is 

 eight or ten days old ; the latter bud forth from th.e hinder lateral angles of some of the 

 abdominal segments, and (like the parts of the mouth) are modified considerably in 

 detail before they acquire their ultimate shapes (Joly). 



