48 INTERNAL ANATOMY OF INSECTS. 
visible. — Before 1 bid adieu to this subject, I must say a 
few words upon the situation of the organs in question 
in the myriapods. In lulus, in each segment is a pair of 
orifices which have usually been regarded as spiracles, 
but M. Savi found that these orifices opened into vesicles 
containing a fetid fluid, and upon a very close examina- 
tion he discovei-ed the real spiracles above the base of the 
legs, in connexion with tracheae 3 . In some of the larger 
species of Scolopendra? large open spiracles in the same 
situation are extremely visible 5 . Cermatia presents a 
singular anomaly: — a single series of spiracles of the 
usual form, each planted in a cleft of the posterior mar- 
gin of the dorsal scuta, runs along the back of the animal c : 
unless we may suppose that, like the seeming spiracles 
of lulus ]ust mentioned, these are merely orifices by which 
it covers itself with some secretion. 
6. A few words upon the number of spiracles. — If you 
examine the common dog-tick [Ixodes Ricinus), you will 
find only one of these organs on each side of the abdo- 
men d ; the Libellulina, as we have seen, have only four, 
all in the trunk ; in the Dynastidcc, Melolontha, and the 
larva of Dytiscus, there are fourteen ; sixteen in the Co- 
prida? ; eighteen in Dytiscus, and probably the majority 
of Coleoptera, both larva and imago, and Lepidoptera ; 
and a pair to each segment except the last, in the My- 
riapods. 
ii. Respiratory plates (Respiratoria). The nearest ap- 
a Osservaz. fyc. sullo I id us foetid. 14 — . 
b They are particularly visible in an undescribed East Indian spe- 
cies, (S. altcrnata K. M.S.) with scuta alternately black and yellow. 
c Plate XXIX. Fig. 20. A". d De Geer, vii. /. \\.f. 3. 
