36 



HARDWICKE'S SCIENCE-GOSSIP. 



remarked to me some while since, nothing of any 

 permanent value in this direction can be done, unless 

 Professor Pictet's types at Geneva, and the types of 

 other nomenclators of the Perlidae elsewhere, undergo 

 a most searching examination. I had hoped that 

 Mr. McLachlan himself would render the scientific 

 world still more deeply indebted to him, by mono- 

 graphing the British species of the family, but as he 

 has published no such work, he probably thinks that 

 the time is not yet ripe for such a performance. 



The Perlidae have been found in Britain in a fossil 

 condition, specimens having occurred, though some- 

 what rarely, in the strata of the Upper Eocene forma- 

 tion. In all probability they will at some future 

 period be proved to be of far earlier origin than is at 

 present supposed, as their anatomical structure points 

 to a primitive organization. 



The earlier naturalists confounded the Perlidae with 



many respects bear a great resemblance to the 

 perfect insects, are usually found in running water ; 

 some species prefer that which is almost or quite 

 stagnant, and others find rapidly-moving streams 

 more suited to their mode of life. Their elongated 

 bodies terminate usually in two many-jointed fila- 

 ments, which, however, become atrophied in certain 

 species, as they attain their adult state. The large 

 head is scaly, and is but poorly provided with masti- 

 catory organs, these serving but little for purposes 

 either of attack or defence. Their forms vary slightly 

 in the different sections. 



These larvae breathe usually by means of sacs 

 attached to the underside of the thorax, these sacs 

 having some resemblance to the organs performing a 

 similar function in Sialid, Phryganid, and Ephemerid 

 larvae. 



The Perlina lame do not, as was once thought, 



Fig. 15. — Ferla maxima, X 4 : c, ccsta ; s.c, sut-costa ; m, medius ; s.m., sub-medius ; a, anal vein. (Original. 



the caddis-flies, with which, however, they have but 

 little in common. The larvae were supposed to 

 possess a like economy to that of Phryganid larvae, 

 long after one Muraldt gave in 1683 a detailed 

 account, accompanied with figures, of the transforma- 

 tions of Perla marginata, in a now rare Latin book 

 entitled, "The Ephemeris of Natural Curiosities." 

 Even the illustrious Linne classed the Perlidae with 

 Phryganidae. The perfect insects of the Perlidae may 

 at once be distinguished from the caddis-flies by the 

 non-possession of any decided hairy covering to the 

 wings, and by the very distinct segmentation of the 

 thorax, which islof greater comparative width than is 

 usual with the Phryganidae. Other distinctive 

 characters are — the possesssion of mandibles and 

 three-jointed tarsi in the Perlidae, whereas the caddis- 

 flies are without mandibles and have tarsi composed 

 of five joints. 



The larvae, which, together with the pupae, in 



construct cases wherein to perform their transforma- 

 tions, and from which they may seize the unwary 

 larvae of May-flies and other aquatic insects which 

 form their food-supply. Their habit is to lie in wait 

 behind stones arid water-reeds, "on murderous 

 thought intent," to surprise and secure their prey. 

 The more brightly-coloured of them effectually con- 

 ceal their whereabouts from most of their enemies 

 by covering their bodies with a layer of mud. 



The pupa resembles the larva, except that it is 

 possessed of rudimentary wing-scales of a leathery 

 texture. When the time arrives for.the final change to 

 take place, it leaves the water, and seeks a suitable spot 

 in which to undergo its transformation. With its sharp 

 claws it takes firm hold of the stone or other resting- 

 place pro tern., and, the skin splitting along the back, 

 the insect emerges, having, with the possession of four 

 reticulated wings, obtained its highest development. 



The perfect insects of both sexes are very inert, 



