50 INTERNAL ANATOMY OF INSECTS. 
. . is2, is a valve 
most probably, as in the case of @istrus Ovis?, 
In the gad-fly of 
that closes the respiratory orifices. 
the ox (Gi. Bovis) there are no plates at the anterior ex- 
tremity of the body; but those planted in the other aie 
are yery remarkable, and demand particular attention. 
Each is separated by a curved line into two unequal por- 
tions; the smallest of which is contiguous to the convex 
belly, and the largest to the concave back of the animal. 
This last is distinguished by two hard, brown, kidney- 
shaped pieces, a little elevated with the concave sides 
turned towards each other: in this sinus is a szmgle, small, 
white spot, which appears to bea spiracle: in the smallest 
portion are ezght minute circular orifices, arranged in a 
line’, As the only communication which this grub has 
with the atmosphere is at its anal extremity, it has no 
occasion for respiratory organs at the other. The gad- 
fly of the horse (Gi. Equi, &c.) which has no communi- 
cation at all with external air, breathing that which is 
received into the stomach, has these plates at doth ends 
of the body. 
lil. Respiratory Appendayes*. These may be divided 
into two kinds ; those by which the animal has zmmediate 
communication with the atmosphere, and those by which 
it extracts air from water. 
1. To begin with the frst. These are often found in in- 
sects which, during their two first states, live in the water. 
No better example, nor one more easy to be examined, 
* Reaum. iv. 555. ¢. xxxv. fi 10. ss. 
® Ibid. 519—. t. xxxvii. f, 3, 4. 
© Prates XVI. Fic. 9. a5. XIX. Fic. 9, 10, 12, 13. a. XXIX. 
Rreeore oe 
