INTERNAL ANATOMY OF INSECTS. ^7 
moth (Hydrocampa stratiotata) at first sight appears to 
be covered on each side with hairs, but which examined 
under a microscope are found to be branching flattish fila- 
ments, each furnished with tubes from the trachea. These 
caterpillars have also the semblance of spiracles, but ap- 
parently found in the usual situation \ The larva of a 
little beetle often mentioned in my letters {Gyrinus Na- 
tator), is furnished on each side of every abdominal seg- 
ment with a long, hairy, slender, acute, conical process, 
of the substance of the segment, through each of which 
an air-tube meanders ; the last segment but one has 
Jour of these processes, longer than the rest b . 
Laminose or foliaceous respiratory appendages distin- 
guish the sides of the abdomen of the larvae and pupse of 
the Ephemera, whose history you found so interesting c . 
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 six 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 d . 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 bronchia: in con- 
nexion with the trachea branching and traversing it in 
all directions, like the veins of leaves 6 . The double ones 
a De Geer i. 526 — . t. xxxvii./. 2 — 6. 
» Ibid. iv. 362—. t. xiii.y. 16—19. 
e Vol. I. p. 282—. II. 365—. 
A See Reaum. vi. t. xlii. — xlvi. and Plate XXIX. Fig. 3—5, 
< Reaum. Ibid. t. xlv./. 2. 
