1920] Hickernell: Digestive System of Cicada 239' 



A gradual increase in the size of the posterior crop during 

 the adult life of the cicada is noticeable. This increase in 

 size is accompanied by a corresponding gradual decrease in the 

 volume of the fat body. This results in the cavernous abdomen 

 of the adult in its final period of existence, a condition especially 

 striking in the male, but also observable in the female during 

 its later history. Since the space necessary for the accommoda- 

 tion of the eggs is much larger than that required to store the 

 sperms, this may account in part for the smaller average size 

 to which the posterior crop attains in the female. 



VI. Discussion. 



The relationship of parts in the digestive system of Cicada 

 orni, as described by Dufour ('33), is unintelligible when the 

 gross anatomy of the organs are alone considered. On the 

 basis of what we have found in sections of the same system in 

 Tibicen septendecim, however, it seems easy to homologize 

 the structures described by Dufour with the corresponding 

 ones in the present subject and to suggest further that the two 

 much-coiled portions of the intestine figured for C. orni are 

 connected by a labyrinth similar to the one described here as 

 the "internal gland." Dufour did not study sections of his- 

 material and ordinary dissection methods would not reveal the 

 relationships which are made plain by sections. If, in C. orni^ 

 there is any difference between the digestive systems of male 

 and female, Dufour's figure is undoubtedly that of a female 

 specimen. At any rate, the digestive apparatus is nearly 

 identical with that of a female Tibicen septendecim. The one 

 slight variation, namely, the point of connection between 

 the ascending intestine and "internal gland," is easily explain- 

 able since the anterior portion of the posterior crop is usually 

 much folded in these forms and the ascending intestine might 

 be so placed between folds, and perhaps in addition have its 

 wall actually grown fast to those of the ascending intestine, 

 so as to appear to empty into the "ventricule chylifique"' 

 (posterior crop). Examination of Dufour's figure of the 

 digestive system of Cicada orni after studying sections of the 

 same in Tibicen septendecim does not leave much doubt as to the 

 similarity of the digestive apparatus in the two species. 



