MECHANISM OF SUCTION IN SCHIZONEURA LANIGBRA. 821 



flunning along the internal face of both stylets is a median longitudinal 

 ridge. This causes two longitudinal grooves to be formed, a dorsal and 

 a ventral groove. 



As the stylets extend towards the extremity of the hypopharynx lip, they 

 gradually approach towards the median line, the longitudinal ridge and 

 the two grooves on the internal face becoming more pronounced, iit the 

 extremity of the hypopharynx lip they meet in the median line, and 

 the two internal faces become apposed. There is thus formed between the 

 stylets two longitudinal canals (figs. 8 and 9) which are more or less separated 

 by the close apposition of the two longitudinal ridges formed on the 

 internal faces. 



I have mentioned before that the tip of the hypopharynx lip possesses 

 a " V "-shaped cleft, owing to the slight prolongation of the two processes 

 which support the openings into the pharyngeal duct and efferent salivary 

 canal. As will be seen in fig. 9, the longitudinal ridges on the internal 

 faces of the maxillary stylets fit into this " V '^-shaped cleft, and the dorsal 

 and ventral canals formed by the junction of these stylets enclose the two 

 processes, thus establishing direct communication with the two canals and 

 the pharyngeal duct and efferent salivary canal respectively. 



The maxillary stylets do not actually fuse when they meet, but towards 

 their extremity they appear to do so, although the line of fusion is clearly 

 marked. 



The compound stylet thus formed possesses two well-marked canals, which 

 run throughout its length : — The dorsal suction-canal, s.c, which conveys the 

 plant-juices to the pharyngeal duct, and thus into the pharynx and a ventral 

 canal. The ventral canal is slightly smaller : it is the salivary ejector canal, 

 ex., and conveys the saliva from the efferent salivary duct into the tissues of 

 the plant. 



Beyond the extremity of the hypopharynx lip, the compound maxillary 

 stylet is supported above in a deep groove on the ventral face of the epi- 

 phtirynx, and below, by grooves on the internal walls of the maxillary 

 sclerites. As is seen in figs. 7, 8, and 9, these surfaces are so arrano-ed 

 that the stylet fits snugly into the grooves, being held firmly in position, 

 at the same time having perfect freedom of movement for protraction or 

 retraction. 



Beyond the region of the epipharynx the maxillary processes and the 

 labrum — which is grooved on its ventral face — afford a firm support for 

 the stylets. 



Towards the extremity of the labrum the compound stylet enters into the 

 longitudinal proboscis-groove and extends along it to the extremity of the 

 proboscis. 



