RESPIRATORY SYSTEM OF THE LOCUST. 267 



dornen; it is held in place by fine muscular bands, as usual; it was not 

 traced beyond the base of tbe abdomen. 



The trachew and dilated air-sacs or respiratory organs, — As the air-tubes 

 and air-sacs are intimately associated with the great powers of flight 

 possessed by the locust, particular attention has been given to their topo- 

 graphical anatomy. The following description is based on a study of 

 living specimens of Caloptenus femur-ruhrum and CEdipoda sordida, as 

 they had to be conducted in the laboratory at the close of the field-work 

 in the West. 



All insects breathe by means of a complicated system of air-tubes 

 ramifying throughout the body, the air entering through a row of spir- 

 acles, or air-holes, or breathing-holes {stigmata), in the sides of the body. 

 There are, as a rule, in locusts two pairs of thoracic and eight j^airs of 

 abdominal spiracles. The first thoracic pair (Fig. 10) is situated on 

 the membrane connecting the prothorax and mesothorax, and is covered 

 by the hinder edge of the protergum (usually called prothorax). The 

 second spiracle is situated on the posterior edge of the mesothorax. 

 There are eight abdominal spiracles, the first one situated just in front 

 of the auditory sac or tympanum (see Fig. 13), and the remaining seven 

 are small openings along the side of the abdomen, as indicated in Fig. 

 IC. From these spiracles air-tubes pass in a short distance and con- 

 nect on each side of the body with the spiracular trachea (Fig. 17, s, Fig. 

 16, s), as we may call it. These spiracular tracheae begin at the posterior 

 spiracle, and extend forward into the mesothorax, there subdividing into 

 several branches. Branches from them pass to the two main ventral 

 tracheae (Fig. IG, v), and to the two main dorsal tracheae (Fig. 17, D, Fig. 

 16, D). The main tracheal system in the abdomen, then, consists of six 

 tubes, three on a side, extending along the abdomen. The pair of ven- 

 tral tracheae extend along the under side of the digestive canal; the dor- 

 sal tracheae rest on the digestive canal. These six tubes are connected 

 by anastomosing tracheae, and, with their numerous subdivisions and 

 minute twigs and the system of dilated tracheae or air-sacs, an intricate 

 net- work of tracheae is formed. 



The system of thoracic air-tubes is quite independent of the abdomi- 

 nal system, and not so easy to make out. The tubes arising from the 

 two thoracic stigmata are not very well marked ; they, however, send 

 two well-marked tracheae into the head (Figs. 17, c, 16, c), which subdivide 

 into the ocular dilated air-tube (Figs. 17, o c, 16, o c) and a number of air- 

 sacs in the front of the head. 



The series of large abdominal air-sacs, of which there are five pairs 

 (Fig. 17,3-7), arise independently of the main tracheae directly from 

 branches originating from the spiracles, as seen in Fig. 16. They are 

 large and easily found by raising the integument of the back. There is ■ 

 a large pair in the mesothorax (Fig. 17, 2), and two enormous sacs in the 

 prothorax (Fig. 17, 1), sometimes extending as far back as the anterior 

 edge of the mesothorax. All these sacs are superficial, lying next to the 



