142 NATURAL HISTOKY. 



The family is pretty well represented in Britain, where several species are well known to anglers;, 

 and supposed to be imitated in those curious productions known as " artificial flies." Thus a rather 

 large brown species, about three-quarters of an inch long (Perla bicaudata], is known as the Stone Fly, 

 and appears in April ; a much smaller green species (Chloroperla viridis), found in May, rejoices in 

 the name of the Yellow Sally, and is also known as the Willow Fly, the latter name being also given, 

 according to Ronald, to a cpecies of Nenmra, probably N. variegata, in which the caudal bristles are 

 rudimentary. The most remarkable circumstance connected with this family is the persistence of 

 branchial tufts in the perfect insects of a small genus, described by the late Mr. Newman under the 

 name of Pteronarcys, species of which have occurred in Canada and Siberia. The genus is 

 distinguished by having all the wing-cells divided up by fine cross-veins ; and branchial tufts to 

 the number of eight pairs are appended to the stigmata of the thoracic segments, and of the first two 

 segments of the abdomen. 



TRIBE SUBULICORNJA. 



The insects which we include under this tribe certainly present many points of divergence, and 

 it is chiefly as a matter of convenience that we have retained the group as established by Latreille 

 and adopted by Burmeister. The character referred to in its name is the form of the antenna?, which 

 are short, awl-shaped, and composed of few joints. The wings are membranous, and generally much 

 reticulated ; the eyes are large, especially in the males ; and the preparatory states, as in the Perlidae, 

 are passed in the water. The differences presented by these insects are very great, and enable us to 

 distinguish two very well-marked families the Ephemeridse, or Day Flies, with very weak or even 

 rudimentary mouths, and the hind wings much smaller than the anterior pair, and the Libellulidae, or 

 Dragon Flies, with powerful mouths, and wings approximately of equal size. 



FAMILY XII. EPHEMEKID^E, OR DAY FLIES. 



The Ephemeridae are delicate, elongated, soft-bodied insects, with a moderate or small head, the 

 surface of which, especially in the males, is chiefly occupied by the large compound eyes, between 

 which are placed two or three ocelli. The antennas, which spring from the forehead below the ocelli, 

 are short and awl-shaped, consisting of two stoutish joints and a minutely-jointed bristle. The parts 

 of the mouth are exceedingly feeble, and, in fact, often membranous in texture, the insect apparently 

 taking no food in the perfect state. The segments of the thorax are very unequal in size, the 

 mesothorax, as might be expected from the gi-eat development of the fore wings, being by far the 

 largest ; the fore wings are somewhat triangular, and the hinder ones rounded, but sometimes altogether 

 wanting, and the principal veins in both pairs are more or less radiating, although branched, and 

 united by numerous cross-veins, so that the wings are generally minutely reticulated. The legs are 

 generally slender, and are terminated by tarsi composed of four or five joints ; the anterior tibiae and 

 tarsi are excessively elongated in the males. In the long slender abdomen eleven segments may be 



recognised, the last of which bears two or three very 

 long, bristle-like jointed filaments, and the last but 

 one in the males is furnished with peculiar sexual 

 appendages. 



These insects, which seem to belong more especially 

 to the temperate climates of the world, are remarkable 

 for the great delicacy of their structure, and for the 

 extreme shortness of their lives in the perfect state, 



EPHEMERA vuLGATA. which seems in general scarcely to exceed a day. 



Hence the name of Ephemeras commonly applied to 



them. Their emergence, which generally takes place in the evening, is followed by a brief dancing 

 existence on the part of the males, chiefly in the neighbourhood of the waters in which their 

 preparatory stages have been passed, and as the insects are always produced in numbers, and the 

 whole of the members of any given species within a district will make their appearance in the course 

 of a few days, the swarms of Ephemera in particular localities are often enormoxis. On the banks 

 of the canals and slow running rivers of tho Netherlands and elsewhere in Europe the air for 

 a few evenings is completely filled with these elegant creatures, and their number is so enormous 



