NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS IO7 



CMcl) arises on the wall of the tergum immediately behind the 

 spiracle, and is inserted on the manubrium of the movable wall of 

 the atrium {q), which projects ventrally and posteriorly. The long 

 opening muscle (OMcl) arises on the lateral edge of the correspond- 

 ing sternum and extends posteriorly and dorsally to its insertion on 

 the manubrium. 



Fig. 54. — Abdominal spiracles of Dissosteira. 



A, first abdominal spiracle, left, outer view. B, inner view of the same spiracle, 

 showing muscles. C, second abdominal spiracle, right, inner view, with tergo- 

 sternal muscles of second abdominal segment. D, eighth abdominal spiracle, 

 right, inner view. 



CMcl, closing muscle of spiracle; ISp, first abdominal spiracle; IIS, second 

 abdominal sternum ; I ISp, second abdominal spiracle ; OMcL, opening muscle 

 of spiracle ; p, anterior margin of tympanal cavity ; q, manubrium of ventral or 

 anterior wall of atrial chamber ; s, movable ventral or anterior wall of atrial 

 chamber ; t, fixed dorsal or posterior wall of atrial chamber ; u, thickening of 

 tergal wall supporting dorsal or anterior wall of atrial chamber ; v, anterior 

 apodemal arm of abdominal sternum; VI IIS, eighth abdominal sternum; VIIISp, 

 eighth abdominal spiracle ; w, posterior angle of tympanal cavity. 



The grasshoppers are abdominal breathers. A discussion of the 

 mechanism of respiration would, therefore, lead too far beyond 

 the anatomical limits of the present paper. Recent studies on the 

 breathing of Orthoptera give such varied and conflicting results that 

 we must conclude either that the subject still needs a critical investi- 

 gation or that the insects have no fixed methods of respiration. 

 The weight of evidence is rather in favor of inconsistancy on the 

 part of the insects. 



