Vlll 



Wabble fly, 



continued (see fig. 5, p. 7) to be that of a pair of short horny, some- 

 what bent cylindrical, or partially cylindrical, tubes, covered at the 

 end (fig. 6) with round or oval discs, which appear to have a definite 

 narrow border, and across the centre of the disc to be of a sieve-lilie or 

 spotted appearance. Fig. 7 precisely represents the appearance when 



Fig. 6. 



Fig. 7. 



Fig. 6.- 



-Spiracle-tube (one of the pair), much magnified. Fig. 7. — Discs at 

 extremity of spiracle, as seen with quarter-inch object-glass. 



much magnified. These discs may amount to as many as about six- 

 and-twenty on each spiracle, and appear to me to be placed each at 

 the extremity of short cylinders. Whether the spotted or sieve-like 

 appearance is caused by minute hairs placed so to preserve the delicate 

 tubes from the entrance of foreign bodies, I had not sufficiently high 

 microscopic powers to ascertain. Up to the time when the moult takes 

 place to the final form, these spiracles were in all the specimens I 

 examined buried up to their disc-covered tips in the tail-end of the 



Fig. 8. — Spiracles fully developed, magnified. 



maggot ; then they are cast entirely with the moulted skin, and in the 

 newly exposed surfaces beneath we find the first appearance of the well- 

 known kidney-shaped spiracles (see fig. 8), but (in the specimens I 

 examined) with the surface somewhat more radiated, and the colour of 

 a paler chestnut than in their later condition. 



The changes of condition appeared to be rapidly gone through, 

 and it was when the maggot has gained about a quarter or third of 



