48 INTERNAL ANATOMY OF INSECTS. 
Before I bid adieu to this subject, I must say a few words 
upon the situation of the organs in question in the my- 
riapods. In Iulus, in each segment is a pair of orifices 
which haveusually been regarded as spiracles, but M. Savi 
found that these orifices opened into vesicles containing 
a fetid fluid, and upon a very close examination he dis- 
covered the real spiracles above the base of the legs, in 
connexion with ¢rachee*. In some of the larger species 
of Scolopendr@ large open spiracles in the same situation 
are extremely visible. Scutigera Lam. (Cermatia Illig.) 
presents a singular anomaly :—a single series of spiracles 
of the usual form, each planted in a cleft of the posterior 
margin of the dorsal scuta, runs along the back of the 
animal*: unless we may suppose that, like the seeming 
spiracles of Zulus just mentioned, these are merely ori- 
fices 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‘; the Lzbellulina, as we have seen, have only four, 
all in the trunk; in the Dynastide, Melolontha, and the 
larva of Dytiscus, there are fourteen ; sixteen in the Co- 
pride ; 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. 
u. Respiratory plates (Respiratoria). The nearest ap- 
* Osservaz. §c. sullo Iulus fetid. 14—. 
> They are particularly visiblein an undescribed East Indian species 
(7. alternata K. M.S.) with scuta alternately black and yellow, 
> Prare XXIX. Fre. 20. 4”, " De Geer, vii. #. vi. f. 8. 
