4-8 INTERNAL ANATOMY OF INSECTS. 



visible. Before I 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 discovered the re*al spiracles above the base of the 

 legs, in connexion with tracheae a . 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 just 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 DyftasticUe, Melolontha, and the 

 larva of Dytiscus, there are fourteen ; sixteen in the Co- 

 pridce , 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. sutto lulus foetid. 14. 



b They are particularly visible in an undescribed East Indian spe- 

 cies, (S. alternata K. M.S.) with scuta alternately black and yellow. 

 c PLATE XXIX. FIG. 20. A'. u De Geer, vii. /. vi./. 3. 



