MERK : MOUTH-PARTS OF THE HEMIPTERA. 271 



second, by the fusion of these parts with the canal from the 

 pharynx. The canals themselves remain distinct and termi- 

 nate at the distal end in delicate processes. 



At the point where the fusions take place a horny ring is 

 formed, and this Gerstfeld makes mention of in the following 

 words : 



"Vorn am Kopfe, fast in gleicher Hohe mit der nach aussen 

 daran liegenden Basen der Mandibeln und etwas uber denselben 

 Theilen der Maxillen sieht man, wie es scheint, bei alien Hem- 

 ipteren ein horniges oder lederartiges Stuck ein wenig vorragen, 

 welches nach dem Vorgange Savigny's von alien Naturforschern 

 als Zunge oder Hypopharynx gedeutet worden ist. Es bildet 

 den untern Theil des vordern Randes eines mehr oder weniger 

 kurzen, hornigen Ringes, welcher den Anfang des Verdauung- 

 kanales rohrenformig umgiebt und tiefer in den Kopf hinein- 

 dringt als die Mundtheile." 



Gerstfeld and Burmeister both agreed in considering this part 

 as an enlargement of the beginning of the alimentary canal 

 rather than a fusion of the epi- and hypopharynx. They were 

 correct in not referring its origin to a fusion of the epi- and 

 hypopharynx, but only partly correct in their other conclusion, 

 since they knew nothing of the salivary injector and its outlet. 

 It is necessary that the pharyngeal and the salivary canals be 

 kept distinct. At the same time, it is equally necessary that 

 they be brought as closely as possible together. The point 

 where they are first bound together shows a natural enlarge- 

 ment. Beyond this point the two tubes are thin and delicate, 

 and extend forward until they are entirely surrounded by the 

 encircling maxillary canals, which, it will be remembered, are 

 made Vjy the grooves in the concave side of the maxillge. The 

 horny ring, then, is not formed by the epi- and hypopharynx 

 uniting to make the beginning of the tubular pharynx, but it is 

 caused by a junction of the canals from the salivary injector and 

 the pharynx. 



PHYSIOLOGY OF THE PARTS. 



Having described each organ in detail, we are now ready to 

 discuss their functions. Before doing this, in order to get an 

 idea of the parts as a whole, it is desirable to trace the lamellj3e 

 invaginated to form the mouth-parts from the exterior surface 



2— Bull. No. 9. 



