March, 1919- 1 Vinal: Carolina Locust. 23 



keeping the tracheae permanently open without affecting their flexi- 

 bility. These elastic threads are not found in the ultimate branches 

 of the tracheae, called tracheoles or in the air sacs. 

 II. General Morphology of the Tracheal System. 



A detailed description of this system would require a very lengthy 

 paper. It is therefore advisable to consider only the more important 

 tracheae found in the Carolina locust in the present article. 



The tracheal system of the grasshopper may be divided into three 

 distinct parts — 



( 1 ) Cephalic tracheae. 



(2) Thoracic tracheae. 



(3) Abdominal tracheae. 



These will be treated separately in the following pages. 



(a) Cephalic Trachecc. 



As we have seen, the first thoracic spiracle (Plate IV, Fig. 11) is 

 composed of two chambers which give rise to two tracheal tubes. 

 The upper chamber or larger opening leads into a large main tube 

 which soon divides, forming two main tracheae which run to the 

 head. The dorsal branch, termed the superior cephalic trachea 

 (Plate II, Fig. 1, /,) runs to the dorsal surface of the head and joins 

 the ophthalmic trachea (Plate III, Fig. 5; ot) surrounding the com- 

 pound eye at the vertex (Plate IV, Fig. 10). The second branch, 

 known as the median cephalic trachea, soon divides and sends a 

 branch to the external lateral head muscles (Plate I, Fig. 5; I 2a ). 

 This also connects dorsally with the superior cephalic trachea and 

 ventrally with the anterior tentorial arm plexus (Tp), as shown in 

 Fig. 5. The other branch of the median cephalic trachea (Plate III, 

 Fig. 1 ; I.,,,) passes through the occipital foramen with the alimentary 

 canal and divides, forming two branches at the main body of the 

 tentorium. One branch (Fig. 1, I., h ') travels along the anterior edge 

 of the dorsal tentorial arm giving off numerous small branches to 

 the muscles and ends in a large air sac {A) situated over the ali- 

 mentary canal (also see Plate IV, Fig. 14). The second branch of 

 I,, 1, ( Fig. 1, 1 ,,.!' ) extends forward and gives off a small branch 

 closely applied to the proventriculus while the main tube runs to the 

 under surface of the brain. Here it forms a large number of vesicu- 

 lar air sacs, which completely surround this organ. Just before the 



