EXTERNAL ANATOMY OF INSECTS. 715 
of the larva of Agrion and of some Diptera is furnished? ; 
the same part in that of Dytiscus ends in a pair of taper- 
ing organs, fringed on each side like the hind-legs of the 
imago, which doubtless assist it in swimming; those 
respiratory foliaceous laminze which so singularly di- 
stinguish the abdomen of the larvee of Ephemera, like 
the legs of the Branchiopod Crustacea, are probably 
used in some degree as fins, and aid their motions in 
the water °. Under this head may also be mentioned 
the many-jointed bristles that form the long tails* of the 
fly that proceeds from these larvee, 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*, and probably, as its leaps are almost as 
long as flights, for a similar purpose, to steady their 
motion. I may here lastly state that I once saw a Cry- 
ptophagus, 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 accom- 
plished its purpose. 
4. Organs of Prehension'. ‘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 
* See above, p. 153. 
> Prate XVIII. Fic. 5. a. 2 
° Prate XXIX. Fic. 3,4. De Geer, ii. t. xvii. f. 12. and ¢. xviii. 
> 9 
4 Ibid. @. xvi. f. 8—13. 
© Prac ewe iG. 16.8)" 
t Ibid) Bier I2 2, 
