DIGESTIVE SYSTEM OF PERIODICAL CICADA. 211 



excreta could hardly fail of notice. Their absence, therefore, 

 can hardly be other than highly significant of the lack of active 

 digestive operations during adult life, and is in entire accord with 

 the fact of the entire absence of alimentary elements in the tract 

 as above cited. 



During the progress of this work my attention was called to 

 a popular paper by R. E. Snodgrass on the Seventeen Year 

 Locust (Smiths. Rept. for 1919, Washington, 1921, pp. 381-409), 

 in which there appear certain views rather sharply in conflict 

 with those herein maintained, and which call for some brief 

 attention. Its anatomical points are reviewed by the junior 

 author in the section which follows. But it falls to me to notice 

 phases of feeding habits and others of a physiologic nature. In 

 reply to certain inquiries submitted to Snodgrass he was kind 

 enough to write me quite freely as to the questions, and also sent 

 a specimen of transected insect to show the highly cavernous 

 aspects of late life, and to afford what was suggested as a demon- 

 stration of the tracheal nature of the so-called "air-chamber." 

 This, I examined with care, but cannot accept as demonstrative, 

 since there were no distinct evidences of its tracheal structure, 

 as the junior author conclusively shows in the histologic demon- 

 strations of all phases of the typical and deteriorative epithelial 

 cells occurring, and an entire absence of chitinous elements or 

 taenidia in the organ. 



Of this "airchamber" Snodgrass states that it "receives its 

 supply of air directly through the spiracles of the first abdominal 

 segment." If this were so there should be unmistakable evidence 

 of its being a paired organ, as in the bee; but of this there is no 

 evidence whatsoever, a fact which he admits but claims such to 

 be the case in the dog-day cicada. This I have not been able to 

 discover from actual dissections, or from serial sections of the 

 regions, as shown by Hickernell in the earlier paper. 



Referring to its function as related to the respiratory system 

 Snodgrass without hesitation discredits the view of Graber, that 

 it may have some relation to the tympanal organs, but says, 

 "We shall probably have to fall back on the old prosaic explana- 

 tion that bulk of body is maintained with corresponding weight 

 eliminated a combination specially favorable to aerial life." 

 But as Packard long ago pointed out (cf. p. 457), this assumption 



