716 EXTERNAL ANATOMY OF INSECTS. 



of the larva oiAgrion and of some Diptera is furnished 3 ; 

 the same part in that of Dytiscas ends in a pair of taper- 

 ing organs, fringed on each side like the hind-legs of the 

 imago b , which doubtless assist it in swimming; those 

 respiratory foliaceous laminae which so singularly di- 

 stinguish the abdomen of the larvae of Ephemera, like the 

 legs of the Branchiopod Crustacea, are probably used in 

 some degree as fins, and aid their motions in the water c . 

 Under this head may also be mentioned the many-jointed 

 bristles that form the long tails d of the fly that proceeds 

 from these larvae, whose interesting history I long since 

 enlarged upon ; for when they fly the two lateral ones 

 diverge from the central one, and perhaps perform the 

 same office as the tail feathers (rectrices) of birds. These 

 bristles are also to be found in Machilis e , and probably, 

 as its leaps are almost as long as Jlights, for a similar 

 purpose, to steady their motion. I may here lastly state 

 that I once saw a Cryptophagus (Corticaria Marsh.), but 

 I forgot to note the species, walking upon my window, 

 which when it wanted to turn fixed itself to the glass by 

 an inflated anal vesicle, and so accomplished its purpose. 

 4. Organs of Prehension f . The abdominal organs of 

 prehension are various ; but as the great body of them are 

 connected with the sexual intercourse of insects, I shall 

 not consider them till I come to treat on that subject. 

 The only remarkable one that is common to both sexes 

 is that of the earwig, which is too well known to every 

 child to call for any long description. The external or- 



» See above, p. 154.- *> Plate XVIII. Fig. 5. a. 



c Plate XXIX. Fig. 3, 4. De Geer, ii. L xvii. /. 12. and t. xviii. 

 /■ 2. J Ibid. t. xvi. / 8—13. 



e Plate XV. Fig. 16. S" . * Ibid. Fig. 12. L". 



