ACRIDIIDAE 



283 



body are not completely developed, or are temporarilj^ diminished. 

 Although air vessels are absent in the neighbouring groups of 

 Orthoptera, Dufour says they are present even in apterous forms 

 of Acridiidae, but he gives no particulars.-"- Packard has given 

 an account ^ of the arrangement of these remarkable sacs in the 

 Eocky Mountain Locust. He finds that there are two sets : a 

 thoracic group, consisting of a pair of very large size, with which 

 are connected some smaller sacs placed in the head ; and an 

 abdominal set, which forms a very remarkable series. The 

 figures we give (Fig. 176, A, B) show that these sacs are of such 

 large size that if fully distended they must interfere with the 

 development of the ovaries, and that they must be themselves 

 greatly diminished, if not obliterated, by the distension of the 

 alimentary canal. "We may look on them 

 as only coming into full play when the 

 normal distension of the canal is prevented, 

 and there is only small development of the 

 reproductive organs. Under such circum- 

 stances the locust becomes a sort of balloon, 

 and migrates. In addition to the air sacs 

 there are many dilatable tracheae, placed 

 chiefly in parts of the body -where there is 

 not space for the large air sacs. These are, 

 for the sake of clearness, omitted from our 



figure. 



The ganglia constituting the brain are 

 simpler in Acridiidae than they are in the 

 higher Insects, such as bees and wasps, and 

 have been specially studied by Packard ^ 

 and Viallanes.* The other ganglia of the Fig. 169.— Ovaries of Oedi- 

 nervous cord are eight in number, three ^"j^"^. ."j'"its''^gut-iike 

 thoracic and five abdominal. appendage ; c, sebiflc 



„, gland; d, termination of 



The salivary glands are small, ine i^^^y ^^fter Dufour.) 

 alimentary canal is capacious but not 



coiled. It has no gizzard, but the crop has a peculiar structure, 

 apparently as a substitute. There are diverticula connected 

 with the true stomach. The Malpighian tubes are elongate 



1 Mem. Ac. Sd. ttrang. vii. 1834, p. 274. 



= First Ann. Rep. U.S. Ent. Comm. 1878, p. 271. 



2 Rep. U.S. Ent. Comm. ii. 1880, p. 223. * Ann. Sci. Nat. (7) iv. Zool. 1887. 



