50 ' INTERNAL ANATOMY OF INSECTS. 
spines replace the prominences a . In Echinomyia grossa 
and others the anal plates appear not to be perforated, 
being surmounted only by a central boss b ; but this, 
most probably, as in the case of (Estms Ovis c , is a valve 
that closes the respiratory orifices. In the gad-fly of 
the ox {CE. Bovis) there are no plates at the anterior ex- 
tremity of the body ; but those planted in the other end 
are very 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 single, small, 
white spot, which appears to be a spiracle : in the smallest 
portion are eight minute circular orifices, arranged in a 
line d . 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 (Gastcrophiliis Equi, &c.) which has no 
communication at all with the external air, breathing that 
which is received into the stomach, has these plates at 
both ends of the body. 
iii. Respiratory Appendages e . These may be divided 
into tvoo kinds ; those by which the animal has immediate 
communication with the atmosphere, and those by which 
it extracts air from water. 
n Plate XIX. Fig. 11. a. b Reaum. iv. 375—. t. xxvi./. 7, 8. 
c Ibid. 555. t. xxxv. /. 10. ss. 
<i Ibid. 519—. t. xxxvii./. 3, 4. 
« Plates XVI. Fig. 9. a b. XIX. Fig. 9, 10, 12, 13. a. XXIX. 
Fig. 3—7. 
