164 



ANATOMY. 



larvae which live constantly in water, but Kirby and Spence * again 

 denied it, their attention being probably drawn to it by Roesel's f 

 observation of their respiration through the anus. This intestinal 

 respiration Suckow J has confirmed by showing branchiae in the colon, 

 and thus proved the entire inutility of spiracles. But in the perfect 

 insect there are seven pairs of spiracles upon the central abdominal 

 segments, which are covered however by the margins of the dorsal 

 plates lapping over them as they lie in the soft connecting membrane. 



In the Termites the spiracles are found in analogous situations, but 

 those of the abdomen are so small that they are seen with difficulty. 



The remaining three orders very closely agree both in the structure 

 of the thorax as well as in the situation of the spiracles. All possess 

 our in the thorax, two of which are upon the limits of the pro-? 

 thorax, between it and the meso- thorax, and the other two lie between 

 the meso- and meta-thorax. In the Hymenoptera, in which the thorax 

 consists of a hard horny case, and the segments are closely united 

 together, the posterior pair of spiracles lie upon the meta-thorax itself, 

 whereby they distinguish themselves from all the other orders ; besides 

 which the anterior pair of spiracles are covered by a small scale-shaped 

 projection of the posterior margin of the pronotum, which scale (tegula, 

 comp. 77-) li es precisely beneath the anterior wing, and is very 

 readily recognisable in the wasps. In PI. XII. No. I. f. 1., wherein the 

 thorax of Cinibcx is represented, the letters a and /3 point out the situa- 

 tion of the spiracles, as also in the same plate, No. II. f. 2. in the thorax 

 of a Scolia. The spiracles of the Lepidoptera are distinguished only by 

 possessing a narrow, scarcely perceptible, horny ring, which lies con- 

 cealed beneath the hair (PI. XIII. No. IV. f. 2. shows at a and /3, 

 where they are placed.) In the Diptera they appear as short, some- 

 what compressed tubes, particularly the first, between the pro- and 

 meso-thorax, as is shown in PI. XIV. No. I. f. 2. in Tabanus, and 

 No. II. f. 2. in Myopa. A similar uniformity exists in the situation 

 of the spiracles of the abdomen, for they always lie in the connecting 

 membrane of the segments, and are covered by the projecting margins 

 of the dorsal plates. 



The numbers of the spiracles are thus shown in their situation. If 



* Introduction to Entomol., vol. iv. letter xxxviii. 



f Insectenbelustigungen, 2 band. Wasserinsecten der 2 classe, Taf. II. r.nd III. 



Reusing. Zeitschr. fur die Org. Physick. 2 band. 2 lift. S. 36, &c. PI. I. and II. 



