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 (Estrus 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 w r ith 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 (Gasterophilus 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 two kinds ; those by which the animal has immediate 

 communication with the atmosphere, and those by which 

 it extracts air from water. 



* PLATE XIX. FIG. 11. a. b Reaum. iv. 375. t. xxvi./. 7, 8. 

 c Ibid. 555. t. xxxv. /. 10. . 

 d Ibid. 519. t. xxxvii./ 3, 4. 



PLATES XVI. FIG. 9. a b. XIX. FIG. 9, 10, 12, 13. a. XXIX. 

 FIG. 37. 



