THE HEMIPTERA 



169 



rostrum is a sheath which appears in the main to be derived from the 

 labium or hinder hp of the chewing insect, being much elongated, and 

 its sides rolled forward to meet or almost meet in front, forming a 

 tube. The front part of this tube, however, near the head, seems not to 

 be formed by the labium, leaving open a somewhat triangular place 

 and the labrum or front lip appears to have grown downward to more or 

 less completely close up this portion of the sheath. Within the tube 





.Mid 



^-la 



Fig. 159. Fig. 160. 



Fig. 159. — Side view of a Squash Bug {Anasa tristis De G.) showing the rostrum, 

 and its attachmentto the front of the head. Some of the mouth parts usually within the 

 sheath have been pulled out and show in front of it. Rather more than twice natural size. 

 {Original.) 



Fig. 160. — Diagram of a cross-section of rostrum of a Squash Bug: la, labium; md, 

 mandible; mx, maxilla: Sa, tube carrying saliva to the wound; su, tube through which the 

 food is drawn into the body. (Modified from Tower, Am. Ent. Soc. Am. VI, 1913.) 



thus formed lie the mandibles and maxillae which have become trans- 

 formed into long and slender bristles with pointed tips. The surfaces 

 of the maxillae which face each other have so changed their outline as to 

 form two gutters or troughs and when the maxillae are pressed together 

 as is the case in the living insect, each gutter of one side coincides with the 

 corresponding one of the other to form two tubes, half of each being 

 contributed by each maxilla. The more anterior of the tubes is for suck- 

 ing the nourishment obtained, into the bug, while the other is for inject- 

 ing saliva into the wound. The mandibles lie beside the maxillae and 

 seem to function chiefly as piercing organs. 



In feeding, the tip of the rostrum is brought into contact with the sur- 

 face of the object to be fed upon and the tips of the mandibles and maxillae 

 are then driven into it until sap or blood as the case may be, is reached. 

 Then saliva is forced into the wound and this seems to be irritating or 

 even poisonous in its nature and its presence in the wound causes (in 

 animals at least) an increased flow of the body fluids to that point. 

 Assured thus of a sufficient supply of food, sucking it into the body of 

 the insect is then begun. 



The eggs of Hemiptera are laid under greatly differing conditions. 

 Some are inserted in twigs or stems; others are laid either singly or in 



