94 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



The description of the basal parts of the abdomen of the cicada 

 given by Vogel (1923) in connection with his account of the chordo- 

 tonal organs, though minute in detail, is not morphologically sound in 

 every respect. The anterior plate of the second sternum (fig. 30 C, /) 

 Vogel regards as the first abdominal sternum, and he consequently 

 refers the tympana and the second spiracles to the first abdominal seg- 

 ment. The posterior sclerite of the second sternum (IIS), bearing 

 the " auditory capsules " (h), he calls the second sternum. Much of 

 this interpretation is clearly in error since it disregards the true first 

 sternum and the first abdominal spiracles, which latter Vogel assigns 

 to the thorax. The difficulty of properly disposing of the first ab- 

 dominal spiracles in the cicada arises from the fact that the spiracular 

 peritremes in the adult insect are fused with the lower posterior 

 margins of the metathoracic postnotum (fig. 30 B, C, FN3), the lower 

 ends of which are united with the epimera ; but the observation that 

 the spiracles in question lie behind the internal intersegmental ridge 

 bearing the lobes of the third phragma shows conclusively that 

 these spiracles belong to the first segment of the abdomen. The true 

 relations of the basal parts of the cicada's abdomen are unmistakable 

 in the mature nymph of Magicicada (D). The first abdominal sternum 

 is here a simple triangular plate (IS) lying immediately behind the 

 metathoracic subcoxae, and the first abdominal spiracles {ISp) lie 

 in the membranous lateral parts of the dorsum of the first segment. 

 The tergum and sternum of the second segment (IIT, IIS) show 

 no particular modifications, and the ventral tympanal cavity is not 

 developed in the nymph. 



One of the most curious aberrations in entomological morphology 

 is the tendency to regard the great air chamber of the cicada's abdomen 

 as a part of the digestive system. The chamber is a thin-walled sac 

 always filled with gas, but never containing liquid. Yet, the cicada's 

 stomach may be distended with liquid food. The idea that the air 

 sac is a diverticulum of the stomach was first proposed by Hickernell 

 (1920) on the basis of histological sections, which seerned to show 

 a connection between the two organs. The question was later dis- 

 cussed in the affirmative by Hargitt (1923) and by Myers (1928). 

 If the air sac lacks taenidia and even a chitinous lining these points 

 do not prove that it is not of tracheal origin, since tracheal sacs do 

 not usually contain taenidia, and some investigators have failed to 

 find chitin in their walls. The abdominal air sac of the cicada, as may 

 be more clearly seen in other genera than Magicicada, opens directly 

 to the exterior through the first abdominal spiracles ; and in various 

 places large, open tracheal tubes are given off from its walls. In 



