MECHANISM OF SUCTION IN SCHIZONBDRA LANGIERA. 315 



nmscle, p.771., they become continuous at their proximal ends, by means of 

 thinner chitin, with the middle o£ the transverse plate *. 



A narrow curved rod of chitin, mx.l., articulates at the proximal end 

 of each niaxillary sclerite, where that structure fuses with the general wall 

 of the fore-head, and near the base of the mandibular lever on each side. 

 They both pass inwards to become attached to the proximal ends of the 

 internal or ventral stylets (maxillary stylets), and thus form the maxillary 

 levers, mx.l., figs. 2, 3, and 17. 



C. The Labium. 



The proboscis or labium Qbm.) is formed by an evagination of the integu- 

 ment at the infra-posterior end of the head. In repose it lies closely 

 adpressed against the ventral surface of the body, between the coxse, and 

 extends for some distance beyond the third pair. It consists of three 

 segments, text-fig. 2, a long proxiuial segment and two shorter distal 

 segments. Its dorsal or anterior face is folded to form a median, longi- 

 tudinal groove, which extends along the greater part of its length. At the 

 extremity of the distal article the walls of the fold close completely over, 

 thus forming a short tube, but throughout the rest of its length the groove 

 is open. The [)roximal end of the proboscis is composed of thin, flexible 

 chitin, as is ^hown in fig. 1. It is this part which is capable of being drawn 

 into the body during feeding, as will be explained later. This proximal end 

 is not grooved. When specimens are examined, the stylets are usually 

 found lying in the proboscis groove, being held in it by the short, closed 

 tube at its extremity. They are often found extending through the end of 

 this tube, beyond the tip of the proboscis. The distal article of the proboscis 

 bears on its extremity a ring of tactile hairs. Daring feeding, the proboscis 

 is raised from the surface of the body, and its anterior face is closely 

 pressed against the hypopharynx and maxillary processes. 



D. The Pharynx. 



The pharynx {ph.) extends through the head iu the median line, and passing 

 over the transverse plate of the tentorium, leads into the oesophagus, fig. 1. 



When a cleared potash preparation of the head is examined from the 

 dorsal aspect, two conspicuous prominences are seen at the anterior end of 

 the pharynx. These are the 2^harynx iirotaherances, p.p., figs. 12, 13. They 

 are the " Naroiden " described by Dreyfus (1894) in Phylloxera. It is in 



* Mordwiiko (1895) lias described these rods iu Lachnus, as the " Chitinfortsatzestabchen." 

 He considers they are free at their proximal ends. By means of serial sections I have 

 traced these rods in Schizonettra to the transverse plate to which they are attached by 

 thin chitin. 



