THE PERIODICAL CICADA 



the tongue (Hphv) to pass to either side of the latter 

 organ, but the channel between them here becomes con- 

 tinuous with a groove on the middle of the forward sur- 

 face of the tongue. When the mouth-opening is closed, 

 as it always is in the fully matured insect, the tongue 

 groove is converted into a tube which leads upward from 

 the channel between the second bristles into the inner 

 cavity of the mouth. It is through this minute passage 

 that the cicada obtains its liquid food; but obviously 

 there must be a pumping apparatus to furnish the sucking 

 force. 



The sucking mechanism is the mouth cavity and its 

 muscles. The mouth cavity, as seen in a section of the 

 head (Fig. 122, Pmp), is a long, oval, thick-walled capsule 

 having its roof, or anterior wall (e), ordinarily bent inward 

 so far as almost to fill the cavity. Upon the midline 

 of the roof is inserted a great mass of muscle fibers 

 {PmpMcls) that have their other attachment on the 

 striated plate of the face (C/p). The contraction of these 

 muscles lifts the roof, and the vacuum thus created in 

 the cavity of the mouth sucks up the liquid food. Then 

 the muscles relax, and the elastic roof again collapses, 

 but the lower end comes down first and forces the liquid 

 upward through the rear exit of the mouth cavity into 

 the pharynx, a small muscular-walled sac (Phy) lying 

 in the back of the head. From the pharynx, the food 

 is driven into the tubular gullet, or oesophagus (OE), 

 and so on into the stomach. 



The bases of both pairs of bristles are retracted into 

 pouches of the lower head wall behind the tongue, and 

 upon each bristle base are inserted sets of protractor 

 and retractor muscle fibers. By means of these muscles, 

 the bristles can be thrust out from the tip of the beak or 

 withdrawn, and the bristles of the stronger first pair 

 are probably the chief organs with which the insect 

 punctures the tissues of the plant on which it feeds. As 

 the bristles enter the wood, the sheath of the beak can 



[203] 



