THK OKGANS OK HKSPIRATION. 101 



as in the branchiae, through the plate of the spiracle. Buth were mis- 

 taken, for these spiracles have likewise a central aperture, which leads 

 directly into the stem of the tracheae. This orifice, which is a small 

 transverse incision, lies in the central round plate (PI. XXIII. f. 4. c), 

 and is very small in proportion to the entire spiracle, and may there- 

 fore be easily overlooked ; but Kaulfuss, in his drawings to Sprengel's 

 Treatise, has everywhere indicated them. The exterior margin is, 

 however, by no means perforated, but merely covered with sculpture, 

 just like the exterior oval horny ring. I consider this margin therefore 

 as the pre-formation of the subsequent oval horny ring, the central 

 plate, however, as the two lips of the here still smaller incision. Inter- 

 nally the main stem of the trachea is observed to originate from the 

 circumference of the aperture, a distinct proof that the incision is its 

 orifice (PI. XXIII. f. 4., d.d.). 



124. 



/ 



After noticing the form of the spiracles, the next most important 

 subject is their situation in the body, which is tolerably uniform in the 

 several orders, but there are a few divarications from it, which we may 

 here briefly indicate. 



In the CoJeoptera each segment of the body has a spiracle, or, to 

 speak more correctly, upon the boundaries of every two segments 

 we find one. The first, and generally the largest spiracle, is seated 

 in the uniting membrane of the pro- and meso-thorax, more closely 

 approaching the exterior and lower margin of the former, where it gene- 

 rally remains when those two portions of the body are separated. The 

 second spiracle lies in a very similar situation, namely, between the 

 meso- and meta-thorax, but it is so concealed by the elytra that it can 

 be discerned only upon very close investigation. It is then observed 

 between the two horny plates which we called above (page 81) the 

 anterior and posterior wings of the scapulas. In a state of repose the 

 two plates lie closely together, and thereby completely cover this spi- 

 racle; but upon the expansion of the wings during flight, when the 

 body filled with air distends, this spiracle also quits its concealment, 

 that it may, like the rest, allow air to flow in and out. The concealed 

 situation of this spiracle explains how it has been overlooked, particu- 

 larly as we observe none in the similarly named segment of the larvae. 

 Straus first observed it, and has exhibited it in the cockchafer and in 

 others. The third spiracle lies between the meta-thorax and the first 



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