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 a . Sometimes they are very narrow and nearly 

 linear, as in many pupae of Liepidoptera, and those in 

 the metatliorax 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 Dytiscm oblong 5 ; in Goerius olens 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*, 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 ; or just above it h ; or between two ' : in 



a Chabrier sur le Vol des Ins. c. 1. 454. 



b PLATE XXIX. FIG. 28. A". c Ibid. FIG. 23. 



d Sepp. I. iv. t. ii./. 3. Ibid. t. xiv./. 3. 



' Ibid. 1. \.f. 6, 7- c Ibid. t. \.f. 7, 8. 



h Ibid. t. x./. 6, 7- ' Ibid, v, t. i./. 3. 



