434 



XEUROPTERA 



The anatomy of the nymphs has been treated by Vayssiere, 1 

 who arranges them in five groups in 

 accordance with the conditions of the 

 tracheal gills : (1) The gills are of large 

 size, are exposed and furnished at the 

 sides with respiratory fringes : ex- 

 ample, Ephemera (Fig. 278). (2) The 

 branchiae are blade-like, not fringed, 

 and are exposed at the sides of the 

 body: example, Cloeon(~Fig. 276). (3) 

 The respiratory tubes are placed on 

 the under surface of plates whose 

 upper surface is not respiratory : ex- 

 ample, Oligoneuria garumnica (Fig. 

 279). (4) The anterior gill is modi- 

 fied to form a plate that covers the 

 others : example, Tricorytlius (Fig. 

 282, B). (5) The gills are concealed in 

 a respiratory chamber : example, Proso- 

 pistoma (Fig. 280). The last of these 

 nymphs is more completely adapted 



FIG. 279. Nymph of Oligoneuna J . 



garumnica, France. g. 2 and Sl , for an aquatic life than any other 



two of the dorsal tracheal gills. I nsect at pre sent known ; it WES for 

 (After Vayssiere.) 



long supposed to be a Crustacean, but 



it has now been shown to be the early stage of a may-fly, 

 the sub-imago having been reared from the nymph. The 

 carapace by which the larger part of the body is covered is 

 formed by the union of the pro- and meso-thorax with the sheaths 

 of the anterior wings, which have an unusually extensive develop- 

 ment; under the carapace there is a respiratory chamber, the 

 floor and sides of which are formed by the posterior wing- 

 sheaths, and by a large plate composed of the united nota of the 

 metathorax and the first six abdominal segments. In this 

 chamber there are placed five pairs of tracheal gills ; entrance of 

 water to the chamber is effected by two laterally-placed orifices, 

 and exit by a single dorsal aperture. These nymphs use the 

 body as a sucker, and so adhere strongly to stones under water. 

 When detached they swim rapidly by means of their caudal 

 setae ; the form of these latter organs is different from that 



1 Ann. Sci. Nat. Zool. (6) xiii. 1882, pp. 1-137, pis. 2-11. 



