PSEUDONEUROPTERA. 141 



no common names. They all have flattened hodies, and the abdomen ends in two long 

 appendages. The larvae are aquatic. 



These insects frequent damp, wooded, shaded places, especially along the banks of 

 brooks and rivers, where they are found throughout the summer, usually resting upon 

 the leaves ; the smaller kinds occur the farthest from the water, being less sluggish 

 in their motions than the larger species, i. e., those of Perla and Pteronarcys. The 

 species of the latter genus are remarkable for uniformly being provided with persistent 

 gills, which are little tufts of short, slender filaments, a pair being situated on the 

 undev side of each thoracic, and the first and second abdominal segments. Similar 

 external gills have recently been found to occur in a few other species of the family. 

 The males of Perla differ a good deal from the females, having very short wings. The 

 Perlidse in general have narrow flat bodies, with a large, square prothorax ; the antennae 

 are long and thread-like, and from the end of the body arise a pair of similar-jointed 

 appendages. A peculiarity of many of the species of this family are the soft, mem- 

 branous, toothless mandibles, the flies apparently taking no solid food. The wings are 

 peculiar, the front pair being long and narrow, while the hinder pair are twice or 

 three times as broad. Both pairs are net-veined, there being a good many small trans- 

 verse veins ; when folded they lie flat on the back, extending beyond the end of the 

 body. The tarsal joints are three in number. 



In their transformations the changes of form from larva to imago are rather slight. 

 The larvae are of much the same shape as the imagoes but with strong horny jaws. 

 They do not live in cases, but free under stones and sticks ; the pupae simply differ 

 in having wing-pads or rudimentary wings ; and they are active, like the larvae. The 

 larvae and pupas breathe by tufts of gills on the under side of the thorax. The females 

 are said to carry their little, black, shining eggs in a sac or bag attached to the end of 

 the body. 



There is no common English name for the species of the family Psocid^ collec- 

 tively, but the most familiar member of it is the little book-louse, " death-tick " or 

 death-watch, which is often seen running over books. The winged forms bear a strik- 

 ing resemblance to plant-lice or aphides, as they are of the same size, of much the 

 same shape, their heads, antennae 

 and legs being of nearly the same 

 proportions, while the wings also 

 strikingly resemble those of the 

 aphides in being small, folded roof- 

 like over the body, the hinder pair 

 being smaller than the fore pair 

 with very few veins, and even these 

 disposed somewhat as in those of „ „„„ J ,. \. , „j 



i Fig. 208. — Psoaus Imeatus, enlarged. 



the plant-lice. These insects are 

 common on shaded fences, and the leaves of trees. One species {Psocus novce-scotice) 

 is as large as any we have met, and abounds in New England among the leaves and 

 twigs of evergreen trees, especially the spruce and fir. The nature of their food is 

 not with certainty known, but they probably feed on lichens and dry vegetable matter 

 rather than small living insects. Their movements are active, and when disturbed 

 they will run out of sight around the tree or leaf upon which they are situated. They 

 appear in the winged state late in summer. The species of Goecilia are small and pale 



