PSOCIDAE 399 



family of Neuroptera, have aquatic larvae and wings somewhat 

 similar in form to those of the Perlidae, but the members of the two 

 families cannot be confounded, as the Phryganeidae have hairy 

 front wings and large and contiguous coxae. 



The antennae of the Perlidae are long, very flexible, and com- 

 posed of a very large number of joints. The parts of the mouth 

 vary a good deal. The mandibles and maxillae are usually rather 

 small, and all the parts of the mouth are of feeble consistence or 

 even membranous; the maxillary palpi are, however, well developed 

 and exserted from the mouth, five-jointed. The labium is short 

 and but little conspicuous. The mandibles in some forms are 

 almost membranous, but in other genera they are firmer and are 

 toothed. The labium is composed of a very large mentum, beyond 

 which is a large piece, usually undivided, bearing the four terminal 

 lobes ; the three-jointed palpus is seated on the side of the large 

 middle sclerite, which is no doubt of composite nature. Con- 

 siderable variety as to the lower lip prevails. The head is broad 

 and flat ; there is an indistinctly -indicated clypeus, three 

 more rarely two ocelli, and on each side an eye neither very 

 large nor perfect. The prothorax is free, and has a flat, 

 margined notum. The meso- and the meta- thorax are large, 

 equal segments. The pro-, meso-, and meta-sternum are large 

 pieces ; between the first and second, and between the second 

 and third there is an. intervening membrane. The inetasternuni 

 is much prolonged backwards, and has on each side a peculiar 

 slit; similar orifices exist on the other sterna (Fig. 254, o). 

 Xewport, who has examined them in Pteronarcys, says that they 

 are blind invaginations of the integument ; he calls them the 

 sternal or furcal orifices. 1 According to this naturalist these very 

 peculiar openings pass into the body " as strong bone-like tubes, 

 diverging from the axis to the periphery of the body in the 

 immediate vicinity of some of the principal tracheae, but that 

 they do not in any way communicate with them, as they terminate 

 abruptly as caecal structures." He thinks them analogous with 

 the endo-skeleton of other Insects ; a view which cannot be con- 

 sidered sufficiently established. Laboulbene states 2 that when 

 Perla parisina is seized and placed on its back, it does not move, 

 but emits a liquid at the base of the articulation of the legs. 



1 Tr. Linn. Soc. xx. 1851, p. 433. 

 2 Bull. Soc. ent. France (4), viii. 1868, p. xxxvii. 



