INTERNAL ANATOMY OF INSECTS. 41 
Upon viewing it under a lens, I observed one of the 
convex pectoral spiracles open and shut, and the in- 
terval between two breathings appeared nearly half a 
minute. 
2. With regard to their shape, spiracles vary consi- 
derably. In general we may observe that the abdomi- 
nal ones are usually flat, while those of the trunk are often 
convex 3 . Sometimes they are very narrow and nearly 
linear, as in many pupae of Lepidoptera, and those in 
the metathorax of the sand-wasps (Ammophila) and af- 
finities; at others they are wider and nearly elliptical, 
as in Lucanus and many Lamellicorn beetles : again, in 
Copris they are circular; in Cordylia Palmarum ovate; 
in Dytiscus oblong b ; in Goeriusolens lunulate; in Gony- 
leptes nearly of the shape of a horse-shoe c ; and proba- 
bly many other forms might be traced, if a thorough in- 
vestigation with this view were undertaken. 
3. The colour of spiracles will not detain us long. In 
the caterpillars of Lepidoptera this is often so contrast- 
ed with that of the rest of the body, as to produce a 
striking and pleasing effect. Thus when the body is of 
a dark colour, they are usually of a pale one d ; or if the 
body is pale, they are dark e , or surrounded with a dark 
ring f . This contrast is often rendered more striking by 
their position with regard to the partial colours that 
often ornament caterpillars : in those whose sides are 
decorated by a longitudinal stripe, the spiracles are often 
planted in it s ; or just above it h ; or between two ' : in 
* Chabrier stir le Vol des Ins. c. 1. 454. 
b Plate XXIX. Fig. 28. A". c Ibid. Fig. 23. 
" Sepp. I. iv. t. W.f. 3. • Ibid. t. xiv./. 3. 
» Ibid. t. v./. 6, 7- E Ibid. t. If. 7, 8. 
h Ibid. t. x.f. 6, 7- ' Ibid. v. /. \.f. 3. 
