1920] Hickernell: Digestive System of Cicada 225 



From the above it is evident that there is no agreement 

 as to the necessity of feeding in the adult insect nor has the 

 morphology of the digestive system been worked out sufficiently, 

 in Tibicen septendecim or any closely related forms, to warrant 

 inferences as to functional activity based upon structural 

 conditions. 



III. Material and Methods. 



The observations herein recorded are based upon the period- 

 ical cicada, Tibicen septendecim Linn. Numerous specimens 

 of the so-called dwarf cicada have been collected, but they 

 were not used in this work. Material was collected during 

 June, 1916, by the author in the vicinity of Syracuse. 

 Additional insects were gathered near Moores Hill, Indiana, 

 by Dr. A. J. Bigney. 



The material was fixed in the following fluids: Bouin, 10% 

 formol, sublimate acetic, Gilson, potassium dichromate, and 

 Zenker. In order to insure rapid penetration of the fluids, the 

 integument was slit with a razor on the ventral side, or the head 

 was cut off allowing the fluids to penetrate rapidly from the 

 anterior end. 



Dissections of freshly killed and also of preserved insects 

 were made under the binocular microscope. The dissection 

 method was not sufficient to reveal all of the relationships of 

 the digestive organs so that serial sections of entire insects, 

 as well as of parts of the digestive tube with adhering tissue, 

 were made. 



In making serial sections of entire insects it was necessary 

 to soften the chitinous integument by means of Labarque's 

 solution. After this process the insects were embedded by the 

 double method of Apathy and sections were cut ten microns 

 thick. Such sections were valuable only for determination of 

 general topographical relationships. 



The various digestive organs were dissected out and serial 

 parafline sections 5 microns thick were made in the usual 

 manner. They were stained with hematoxylin and eosin. By 

 means of these sections various relationships were made appar- 

 ent which could not be cleared up by gross dissections. 



