March, 1 9 19-1 VlNAL : CAROLINA LOCUST. 21 



two-lobed valve. The basal portion of the anterior lobe is prolonged 

 somewhat posteriorly, forming a protruding pocket of the body wall. 

 The aperture immediately within the valve is divided into two cham- 

 bers, each of which leads to a separate main tracheal tube. Between 

 these tracheae is a chitinous septum (stm) which arises at the inner 

 side of the posterior valvular lobe and extends anteriorly. Here it 

 is tbickened on its free end to which an occlusor muscle (ocm) is 

 attached. Two valvular muscles are connected to an internal chiti- 

 nous projection which arises at the lower anterior corner of the 

 forward lobe. One muscle is inserted at the thickened end of the 

 septum (see Fig. 11) and is the true occlusor muscle, while the other 

 runs to the outer edge of the posterior lobe. As mentioned above 

 two separate main tracheal tubes arise directly from this spiracle 

 as shown in figure II. The dorsal or larger air tube supplies the 

 cephalic tracheae, while the lower or smaller tube gives off its branches 

 to the thoracic muscles. 



(b) Second Thoracic Spiracle. — (Plate IV, Fig. 12.) This con- 

 sists of an external two-lobed valve, the anterior lobe of which is 

 considerably larger than the posterior one, and leads directly into a 

 single main tracheal tube. Each lobe is somewhat triangular in out- 

 line and their opposing corners are connected internally by a chiti- 

 nous cross band. The occlusor muscle (ocm) is inserted at the 

 middle of this band and extends ventrally to a chitinous projection 

 of the integument. The contraction of this muscle draws both lobes 

 together. 



(c) Abdominal Spiracles. — (Plate IV, Fig. 13.) These differ 

 markedly from the thoracic spiracles, their external orifice being per- 

 manently open and leading directly into a shallow oval cup which 

 communicates with a single main trachea. The occluding apparatus 

 is quite different from those described above and consists of an in- 

 ternal hinged lobe at the apex of which the occlusor muscle (ocm) . 

 is attached. The abdominal spiracles are partly surrounded by a 

 peculiar semicircular horny margin which is merely the infolded edge 

 of the integument surrounding the spiracle. The occluding lobe 

 (left lobe, Fig. 13) is drawn down upon this horny margin by the 

 occluding muscle (ocm), thus cutting off the supply of air to the 

 tracheal tube. 



Each of the eight pairs of abdominal spiracles is constructed on 



