Bt JOttN L. FROGGATT. 6(>5 



the space generally tends to project the inner side of the band 

 inwards. Tliere is no projection of the inner margin of the band 

 between the slits. The slits radiate out from the base, and fill 

 the greater part of the spiracular plate, but do not run the full 

 length of it. In shape, the slits are all very similar, being, as a 

 rule, fairly straight and regular. The "intermediate structure" 

 is well developed, and always present between the middle and 

 inner slits. The "blister-structure" is always present on the 

 slits, and well developed. The blister seems, more noticeably in 

 this species, to be contained in a sheath which generally runs a 

 long way along the slit on either side of the blister: this is 

 generally more pronounced on the middle slit. 



Ophyka nigra. (Plate Ixx., ligs.l, \a). 



Anterior S]) ir acles.— Csup not divided into two parts. Tubules 

 long and slender. 



Posterior Spiracles. — Band complete, and comparatively thick 

 and strong. It is differentiated, in the earlier stages of the de- 

 velopment of the maggot, into two parts, the inner part being 

 the broader and stronger. It is regular in outline. The space 

 is not in the band, but is surrounded by a development of cliitin 

 at the base of the plate, resting against the band. The space is 

 almost completely filled by a development of cliitin. The bases 

 of the inner and outer slits rest against this ingrowth of cliitin. 

 Compared with the size of the spiracular plate, the slits are small, 

 and appear to be well separated from one another. This is due 

 to each slit being surrounded by an envelope of hyaline material, 

 which envelopes are, however, lying up against one another. The 

 inner margin of the band does not, as a rule, project downwards 

 at all between the slits The outer and inner slits are usually 

 fairly straight and regular to almost the upper end, where they 

 bend over slightly outwards an3 inwards respectively. Thev 

 may, however, present a slightly wavy appearance. The middle 

 slit is always wavy in outline, with the tip of the upper end 

 bending slightly over. "Intermediate* and "blister-structures" 

 are absent. 



