FOLSOM : MOUTH-PARTS OF ORCHESELLA CINCTA. 21 



compare to a long, shallow boat, pointed at both ends and somewhat 

 crescentic in transverse section (Plate 4, Figs. 29-32, stp.). The two 

 thickened margins of the stipes are not parallel, however ; the anterior 

 portion of the dorsal margin is twisted toward the median plane of the 

 head, as shown in Fig. 18. The ventral margin, moreover, is sharply 

 incurved, as may be seen in transverse sections of the stipes (Plate 4, 

 Figs. 31, 32). The anterior end of the stipes is rounded where it artic- 

 ulates (Fig. 19, ate.) with the movable head (cpt.) of the maxilla. The 

 stipes is strengthened by a somewhat oblique cross rib connecting the 

 two margins ; the rib is prolonged beyond the dorsal margin as a free 

 projection (Fig. 18, prj.), the function of which I am unable to state; 

 I find no attachment of muscles or other structures upon it. The base 

 of the stipes is immovably fixed to the cardo, the junction being indi- 

 cated by a distinct suture (Fig. 18, sut.). The cardo (Fig. 18, car.) is 

 shaped like a shoe, the toe of which is attenuated to form a chitinous 

 ligament (Figs. 18 and 20, lig.'), which is continuous with a ligament 

 from the foot of the glossa, a suture showing that the now single liga- 

 ment originated from the union of two. By means of this peculiar 

 articulation — already noticed by de Olfers, Tullberg, and von Stummer- 

 Traunfels — and the ligament from the glossa to be next described are 

 permitted the movements of the maxilla as a whole. The toe of the 

 glossa, namely, is extended into a long flexible chitinous ligament (Fig. 

 10, lig.), which is fastened to the outside of the base of the stipes. 

 The length of this outer ligament evidently determines the extent to 

 which the maxilla may be protruded, the supporting stalks of the glossa 

 being stationary. 



The rod of chitin previously mentioned as assisting in the adduction 

 of the head of the maxilla is crescentic in cross section (Plate 4, Figs. 

 29 and 30, bac). Articulating with the base of the rod is a chitinous 

 expansion (Fig. 18, exp.) for the insertion of four muscles. This ex- 

 pansion is nearly A-shaped in cross section (Plate 4, Fig. 31, exp.), 

 there being a dorsal longitudinal ridge with a sloping wing on either 

 side. In the angle between the ridge and the lateral wing is inserted 

 muscle No. 7 of the maxilla. The opposite or mesal wing is prolonged 

 backward in line with the rod (Figs. 18 and 20), and serves for the in- 

 sertion of muscles Nos. 2 and 3. The base of the rod itself is prolonged 

 into a short ligament (Fig. 18, lig.), by means of which the rod is con- 

 nected with the adjacent corner of the base of the paraglossa (Fig. 18, 

 pa'gls.). In order to show the ligament in Figure 18, I have represented 

 the maxilla as withdrawn from the paraglossa. Normally, however, the 



