THE PERLW^E. 



TRIBE PLECOPTERA. 



The insects of this tribe are specially distinguished from all the foregoing by the structure of the 

 s which have the main longitudinal veins united by branches on the disc of the wings so as to 

 form elongated cells, some of which are usually divided by cross-veins, and beyond which the apical 

 part of the wing is traversed by about double the number of finer veins. The hind wings in nearly 

 all are broader than the anterior pair, owing to the greater development of their hinder area ; and in 

 consequence of this they are folded in repose so as closely to wrap the abdomen. The name of the 

 tribe alludes to this character. They form a single family. 



FAMILY XI. PERLID^E. 



Besides the wirg-characters above described, the Perlidse show a rather elongated body, with a 

 head of large or moderate size, bearing a pair of oval eyes, usually three ocelli, of which, however, the 

 foremost is often very small or even quite rudimentary, and a pair of long, tapering, many-jointed 

 antennae. Of the parts of the mouth, the 

 mandibles are generally weak and mem- 

 branous, but sometimes horny and toothed ; 

 the maxilla? ai - e rather small, but show 

 distinctly the two lobes, and bear five- 

 joiiited palpi ; and the labium is cleft in 

 front and furnished with palpi of three 

 joints. Although the wings are well 

 developed, the three segments of the thorax 

 are nearly of equal size ; the legs are 

 powerful, and terminated by three-jointed 

 tarsi, of which the last joint is elongated 

 and bears a large arolium between the 

 claws. The abdomen is composed of ten 

 segments, and has at its extremity a pair 

 of jointed filaments, which are generally 

 of considerable length, but sometimes 

 short or quite rudimentary. In the males 

 the wings are often less developed than in 

 the females, a most unusual sexual differ- 

 ence, which applies sometimes to both 

 pairs, sometimes only to the anterior. 



The species of this family, which are 



all of small or moderate size, are not very numerous, and chiefly inhabitants of the temperate regions 

 of both hemispheres. Their larvae, which closely resemble the perfect insects in general form, 

 except that the prothorax is comparatively smaller, live in running water, and in the larger species 

 are provided with branchial tufts on the under side of the thorax. They creep about upon and 

 under stones, and on the stems of aquatic plants, and are carnivorous in their habits, preying upon 

 smaller aquatic animals, and especially upon the larvae of the Day Flies belonging to the next family. 

 They also swim pretty freely, partly by means of their widened femora, and partly by undulating 

 movements of the abdomen. The insects are believed to pass several years in their preparatory 

 states, in the last (or pupal) stage of which they acquire the rudiments of wings packed away in cases 

 ou the sides of the thorax. When mature they creep up the stem of some plant until they get above 

 the surface of the water, when they rest for a time, until the skin covering the head and thorax splits 

 in the middle line, and the perfect insect creeps forth in a soft state, and with its wings still unexpanded. 

 Even after the full development of the wings, the flight of the imago is slow and of short duration, 



1 j 1 -I . 



3 males in many cases cannot fly at all. The perfect insects are generally found resting quietly 

 on plants and other objects on the banks of the streams in which they have passed their earlier stages- 

 The female extrudes her eggs so as to form a little mass adhering to the end of her abdomen, and this is 

 afterwards dropped into the water during one of the short and sluggish flights performed by the parent. 



PERL A. MARGIN ATA AND ITS PUPA. 



