MECHANISM OF SUCTION IN SCHIZONEURA LANIGERA. 317 



E. The Epipliarynx. 



When exainiiieJ in transverse sections, fig. 9, the epipharynx is seen to be 

 deeply grooved on its internal face, affording, towards its distal end, a kind 

 of bay in which the maxillary stylets are snugly fitted. 



In cleared preparations of the head, fig. 3, the epipharynx is seen to 

 possess a median row of eight well-formed {)ores, and these are also seen in 

 median longitudinal sections, figs. 1 and 25. Drej'fus (1894) has figured 

 and described a similar structure in Phylloxera, and calls it the hypopharynx. 

 He has also figured the eight pores, but considers these " pale spots " as small 

 chitinous pegs. It may not be out of place here to emphasize the need of 

 verifying observations made on cleared specimens by means of sections. 

 The danger of misinterpreting deeply-seated chitinous structures from cleared 

 transparent specimens is very great^ and serial sections are indispensable if a 

 true interpretation of internal chitinous structures is to be gained. 



In longitudinal sections the epipharynx appears as a perforated plate, and 

 is probably the perforated languette described by Bugnion and PopofF (1911), 

 and also by Wedde (1885) in other Hemiptera. 



Lying above the anterior end of the pharynx and extending over the 

 pores in the epipharynx is an irregular group of cells, possessing large, 

 deeply-staining nuclei, but cell-walls are not defined, fig. 25, g.o. 



This structure is found in all sections. Behind the epipharynx it seems to 

 divide into two lobes which extend one on each side ol: the divaricator muscles. 

 In lonoitudinal sections taken a little out of the median line, I have found a 

 nerve passing from the two anterior lobes of the supra-oesophageal ganglion 

 to each lobe of this structure. 



From its position over the perforated epipharynx this structure would seem 

 to be a giistatoTii organ. An organ in this position has been described by 

 Bugnion and PopofF (1911) in Heteroptera, and also by Wedde (1885), but 

 as far as I am able to see with the sections I have made, the histological 

 structure does not agree with the figure given by the former authors. It 

 certainly does not appear to be a glandular structure. I hope in the near 

 future to make special preparations and sections to show the structure of 

 this organ, which will demand the application of special methods. From 

 indirect evidence it would appear that it is an organ of taste, which enables 

 the aphid to test the nature of the sap drawn into the pharyngeal duct 

 before it enters into the pharynx proper. 



That aphids are able to readily appreciate differences in the plant-juices 

 derived from different plants is quite certain from observations I have made 

 this year during the progress of some experiments with Aphis riimicis. 

 There is no other organ present which could exert such a function. The 

 tactile hairs at the extremity of the proboscis only serve to enable the aphis 

 to find a suitable tender part of the plant in which to insert its stylets. 



