50 MOSQUITOES OF NOETH AMEEICA 



are ordinary salivary glands and the third, between the other two, differs in ap- 

 pearance and structure and secretes the poison. Each set of glands discharges 

 into a very fine duct and these ducts unite in the back of the head and continue 

 forward as a single duct through the ventral region of the head. Macloskie's 

 studies were made with Aedes tceniorhyncJius and a species of Anopheles. 



At the base of the hypopharynx is the salivary pump into which the salivary 

 duct empties, to be continued beyond it into the hypopharynx. Macloskie failed 

 to recognize its true character and called it the salivary " reservoir." Its true 

 character appears to have been first recognized by Annett, Button, and Elliott. 

 The organ is fully described by Kuttall and Shipley, from whom we quote. As 

 yet the organ has only been demonstrated in Anopheles. 



"... The structure is more than a receptacle, it constitutes a pump, the 

 mechanism of which corresponds to that of the pharyngeal pump in a sense, that 

 is, it depends upon the action of powerful voluntaiy muscles which overcome the 

 elasticity of a chitinous membrane which, when released by the muscles becom- 

 ing relaxed, rebounds or returns to its original form, as a bow does when the pull 

 on the bow-string is released. ... It will be seen then that the common salivary 

 duct ends (lumen Bfi) in the centre of the chitinous membrane, the junction be- 

 ing strengthened by a chitinous thickening of annular form. The membrane is 

 continuous with a highly chitinized cup, which tapers anteriorly, and is continu- 

 ous with the hypopharynx, an opening therein connecting it with the groove 

 described above. . . . Spicules of chitin occur about the duct on the pump- 

 membrane, these serving for the attachment of the powerful muscles presently 

 to be described. The thickened chitin surrounding the membrane is flattened 

 on its dorsal surface which is applied to the floor of the buccal cavity. The 

 pump-membrane is covered in the centre by the insertion of two stout bundles of 

 muscle-fibres which pass backwards, parallel with one another, to their origin 

 on the anterior surface of the chitinous flange which projects ventrally from the 

 floor of the buccal cavity. When the muscles contract a partial vacuum is 

 produced within the cup, saliva flows in from the glands, and when they relax 

 the membrane rebounds forward, driving the saliva out of the cup into the 

 salivary channel along the hypopharynx." 



Leon, who investigated this organ independently, gives a description at vari- 

 ance with that of Nuttall and Shipley. He found that the salivary duct empties, 

 not into the center of the posterior membrane of the cup, as described by Nuttall 

 and Shipley, but into the side of the chitinous cup. The pumping device Leon 

 describes as follows : 



" The mouth of the cup, which is directed posteriorly and ventrally, is covered 

 by an elastic chitinous membrane which is pushed back into the interior of the 

 cup like the bottom of a champagne-bottle. Outside, in the middle of this mem- 

 brane, a chitinous piston-rod is attached. This has the form of a round concave- 

 convex disc and is more darkly colored ; the convex side of the disc is attached to 

 the elastic membrane, while in the middle of the concave side the rod is fixed. 

 . . . The posterior end of the rod is thickened and muscles are attached to it." 



THE PALPI. 

 The palpi, as they appear in both sexes of Culex, have been described in the 

 foregoing in connection with the other mouthparts. Great diversities of 

 opinion have been expressed by the different students as to their structure and 



