The Basal Sclerites of the Leg in Insects. 3 



as a triangular plate in (Figs. 2, 3, and 22) divided by an oblique 

 suture, into an anterior and posterior region (Figs. 2 and 22, at and 

 pt). The anterior region, at, is the one chiefly concerned in the 

 formation of the articulation with the coxa, the posterior region, pt, 

 being usually, though not always, situated slightly back of this 

 point. 



The true trochantin is always situated in front of the pleural 

 fulcrum of the coxa, and a portion of the episternum (or its homo- 

 logue) always intervenes between it and the pleural suture, although 

 this is not always evident until the specimen has been boiled in 

 caustic potash, and the parts have been spread apart. In some instances, 

 the trochantin is separated from the lower portion of the pleural plate 

 by a membranous area, or by a suture, while in other cases, it is more 

 or less completely united with the lower portion of the pleural plate. 



The following modifications of the typical form of the trochantin 

 are met with in various insects. In the mesothorax of the earwig 

 (Fig. 19) there are two distinct plates, at and pt, which may 

 correspond, in a general way, to the anterior and posterior regions, 

 at and pt, marked oif by the oblique suture in the typical trochantin 

 (Figs. 22, 2 and 3). One of the Avriters of the present paper, 

 however, considers that the sclerite at of Fig. 19, may represent 

 the entire trochantin, while the plate pt may be a new formation, 

 as is the case with the small plate jc of Figs. 19 and 22. 



In the prothorax of the roaches or Blattoidea (and in the pro- 

 thorax of such insects as the Phasmoidea, Isoptera, etc., which are 

 closely related to them) the basal portion of the trochantin, ht 

 (Fig. 1), unites with the lower portion of the pleural plate, while 

 the terminal portion of the trochantin, tnl, becomes detached to form 

 a distinct plate, designated as the trochantinelle, in previous writings. 

 The small plate tnl, is usually incorrectlj' designated as the entire 

 trochantin, while the basal portion, U, is mistaken for a portion of 

 the episternum The basal region, U, however, is separated from 

 the episternum by a well marked suture, in many roaches, and a 

 portion of the episternum, es, intervenes between it and the pleural 

 suture, as is the case in the typical condition of the trochantin; so 

 that it is difficult to understand how such a mistaken conception 

 of the nature of the sclerite in question, could have arisen. 



In attempting to homologize the parts of the region ptn of 

 Mantispa and Corydalis (Figs. 8 and 13) with those of the roach 

 (Figs. 1 and 2), the following points should be observed. The pro- 



