INTERNAL ANATOMY OF INSECTS... 41 
viewing it under a lens, I observed one of the convex pec- 
toral spiracles open and shut, and the interval 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*. Sometimes they are very narrow and 
nearly linear, as in many pupee of Lepidoptera, and those 
in the metathorax of the sandwasps (Ammophila K.) and 
affinities; at others they are wider and nearly elliptical, 
as in Lucanus and many Lamellicorn beetles: again, in 
Copris they are circular; in Calandra Palmarum ovate; 
in Dytiscus oblong®; in Staphylinus olens lunulate; in 
Gonyleptes nearly of the shape of a horse-shoe‘; and 
probably many other forms might be traced, if a thorough 
investigation with this view were undertaken. 
3. The colour of spiracles will not detain us long. In 
the caterpillars of Lepédoptera this is often so contrasted 
with that of the rest of the body, as to produce a strik- 
ing and pleasing effect. Thus when the body is of a 
dark colour, they are usually of a pale one‘; or if the 
body is pale, they are dark®, or surrounded with a dark 
ring‘. 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"; or between two!: 
a Chabrier sue Vol des Ins. c.1. 454. 
> Plate XXIX. Fic. 28. A”. ¢ Ibid. Fic. 23. 
sienee Jie Nera 1G 6 ae eT Gte ed XdVe fue 
# Thid. tov. JG, de SUMO AL Af. 1.4.8 
n Tbid. t. x. f. 6, 7. i [bid. v. t. i. f. 3. 
