266 INSECTS AT nO.ME. 



the best known, is Perla bicaudafa. Then, the familiar 

 ' Yellow Sally ' of anglers is Chloroperla virldls, and the 

 equally familiar ' Willow-fly ' belongs to the genus Nemoura. 



As is the case with many other aquatic insects, the pupse of 

 the Stone-flies crawl out of the water when they are about to 

 assume their perfect state, so that when they come to expand 

 their wings an ample space may be gained for this important, 

 and often perilous, task. The details of this process will bo 

 explained in connexion with the various, species of Nem-opterous 

 insects. 



All the Perlidse have a very moth-like aspect, especially on 

 the wing, and, owing to the invariable sombreness of their hues, 

 and their great similitude in shape, there is considerable diffi- 

 culty in distinguishing between the various species. With 

 many species this difficulty is still more increased by the 

 difference in size between the sexes, the males being scarcely 

 one-third as large as the females, and having wings very short 

 in proportion to the length of their bodies. 



Now we come to another family, the Ephemeridee, better 

 known by the popular name of May-flies. In many respects 

 these are very curious insects, and not the least remarkable 

 point about them is that in the perfect state they have no 

 mouth. The parts of the mouth are certainly there, but in a 

 rudimentary condition, and entirely incapable of receiving 

 food, so that during the time of its existence as a perfect 

 insect, the Ephemera never eats, neither does it require to eat. 



The wings are very unequal in size, the lower pair being very 

 small, and in some species reduced to mere rudiments. In 

 consequence of this formation of the wings, Dr. Leach con- 

 sidered that the May-flies ought to be formed into a separate 

 order, to which he gave the name of Anisoptera, or unequal- 

 winged insects. The end of the body is furnished with either 

 two or three long and slender filaments ; and by these three 

 characters — the mouth, the wings, and the tail — the May-flies 

 may be at once distinguished from all other insects. The best 

 known species. Ephemera vulgata, or Common Mat-fly, is 

 shown on Plate VIII. Fig. 1. 



The transformations of the May-flies are very remarkable, 

 and in some respects almost unique. In its larval condition. 



