May, 1916] Homopteroiis Studies. Part II 307 



is attached by its strong lateral and central muscles to the gula 

 and to the body of the tentorium. The membrane of the 

 proximal joint is developed into a central chitinous rod, to 

 which attach the central muscles (c) ; at the sides the muscles 

 attach directly to the basal joint at one end and to the gula 

 at the other. The labium forms the floor of the mouth, and 

 ■encloses the mandibular and maxillary setae. As the mouth- 

 parts of the Jassid are fitted for sucking, the two pairs of setas 

 are in close relation in the trough which runs the full length 

 of the labium. This trough is shallow, and closed for the 

 greater part beyond the epipharynx. The maxillary setae 

 form the sucking tube through which the plant juices are 

 drawn. It is quite possible that the mandibles form the 

 piercing organs, by means of which the maxilla are enabled to 

 function. Two sets of muscles are to be found in the labium^ 

 ■circular (c. m.) and longitudinal. The longitudinal muscles 

 enable a back and forward movement, such as protrusion and 

 withdrawal, while the circular muscles allow of an up and 

 ■down movement. The attachment of the labium to the gula 

 is not very strong and frequently on removing the head from the 

 body, the labium will remain attached to the anterior edge of 

 the prosternum. The setae are capable of withdrawal from the 

 trough of the labium, and may be free — this is often the case 

 in nymphal forms. At the anterior edge of the labrum where 

 the setae emerge from the head capsule into the labium, a small 

 membrane covers the entrance to the labium, making the 

 ■structure airtight. This is necessary when it is considered 

 that the plant juices constituting the food of the insect must 

 be sucked up into the pharynx. 



The tip of the labium is rounded and the setae are protruded 

 through a small hole at the end. The external region of the 

 labium is chitinized, and is set with numerous hairs or spines. 

 In feeding, the labium is applied to the plant leaf or tissue 

 and forms a guide for the setse. It however, does not enter 

 the plant tissue. It is quite possible that the close application 

 of the labium to the plant will render the connection airtight 

 so that the juices may more readily be sucked up. 



Maxill(B~{V\. XX, Figs. 7, 17, 5, 4, 3). If the head of a 

 Jassid be examined, two large plates (mx. pi.) forming the 

 sides of the face and the lateral covering of the mouth, will be 



