folsom: mouth-pakts of orchesella cincta. 25 



single segment. The extremity is provided with five bristles, each seated 

 upon a tubercle, the proximal bristle and its tubercle being much the 

 largest. The palpus lies dorsal to its maxilla and its base is attached to 

 the chitinous expansion of the maxilla, as represented in Figure 18. It 

 will be noticed that the palpus joins the expansion close to the ligament 

 which unites the chitinous rod (bac.) and the paraglossa (Fig. 18, pa'gls.), 

 so that the ligament might readily be mistaken for a prolongation of the 

 palpus. Careful study shows, however, that the ligament is directly con- 

 tinuous with the rod, and not with the palpus. If the palpus is con- 

 nected with the paraglossa at all, the attachment is only of the most 

 incidental nature. 



The palpus contains at least two longitudinal muscles, which arise from 

 the chitinous supporting structure at its base and extend to its free ex- 

 tremity. The palpus is lined with confluent, deeply pigmented hypo- 

 dermis cells ; beneath the setse are filiform cells, each with an enlarged 

 base which contains a large oval nucleus ; a condition also found in the 

 labrum and labium. 



Glossa and Paraglossa. 



These structures have been briefly mentioned and differently named 

 by several authors. By de Olfers ('62) they were called respectively 

 lingua and organa cochleariformia ; by Lubbock ('62), ligula and second 

 maxillae ; by Meinert ('65), lingua and paraglossce ; by Tullberg ('72), 

 lamina hypopharyngis inferior and laminae hypopharyngis superiores ; 

 finally, by Grassi, Oudemans, and von Stummer-Traunfels, ligula and 

 paraglossce. Careful comparison has led me to believe that the ligula 

 and paraglossa? of Thysanura are the equivalents, respectively, of the 

 glossa and paraglossa? of other mandibulate insects; the Thysanura, 

 however, exhibit the more primitive or generalized condition of tongue, 

 which is not consolidated with the labium. The term ligula, at present, 

 is properly applied to the glossa and paraglossa? taken together, rather 

 than to the glossa alone. 



The paraglossce (Plate 3, Fig. 22, pa'gls.) are two membranous, 

 transparent, chitinous appendages attached to the dorsal surface of the 

 glossa. The basal half of either appendage is firmly united to the 

 glossa, and therefore can have no power of independent movement. 

 The apical half is a free lobe, oval in cross section (Plate 4, Fig. 28, 

 pa'gls.). A paraglossa viewed from above presents somewhat the form of 

 an isosceles triangle with a rounded apex and nearly equalling the glossa 

 in length. The lateral surfaces are strengthened by being thicker and 



