INTERNAL ANATOMY OF INSECTS. 57 
Natator), is furnished on each side of every abdominal 
segment with a long, hairy, slender, acute, conical pro- 
cess, of the substance of the segment, through each of 
which an air-tube meanders; the last segment but one 
has four of these processes, longer than the rest. 
Laminose or foliaceous respiratory appendages distin- 
guish the sides of the abdomen of the larvee and pupze of 
the Hphemere, whose history you found so interesting>. 
In them these organs wear much the appearance of gills. 
In the different species they vary both in their number 
and structure. With regard to their number, some have 
only s¢x pair of them, while others have seven. In their 
structure the variations are more numerous, and some- 
times present to the admiring physiologist very beautiful 
forms‘. ‘They usually consist of two branches, but occa- 
sionally are single, with one part folding over the other, 
as in one figured by Reaumur, which precisely resembles 
the leaf of some plant, the air-vessels or bronchie in con- 
nexion with the ¢rachee branching and traversing it in 
all directions, like the veins of leaves‘. ‘The double ones 
differ in form. In the larva and pupa of Ephemera vul- 
gata there are szx of these double false gills on each side 
of the abdomen, the three last segments being without 
them; each branch consists of a long fusiform piece, ra- 
ther tumid and terminating in a point, which is fringed 
on each side with a number of flattish filaments, blunt 
at the end. An air-vessel from the trachea enters the 
gill at its base; is first divided into two larger branches, 
@ De Geer iv. 362—. ¢. xiii. fi 16—19. 
> Vor. I. p. 279—. I. 369—. : 
¢ See Reaum. vi. ¢. xlii.—xlvi. and Phare XXIX. Fic. 3—5. 
d Reaum. did. é. xlv. f. 2. 
