PROC. ENT. SOC. WASH., VOL. 24, NO. 2, MAR., 1922 69 



other hand, the median outgrowths or endites labeled ce, be, 

 ie, me, etc., borne on the median surface of the coxopodite, 

 basipodite, ischiopodite, meropodite, etc. (which, for convenience, 

 may be termed the coxendite, basendite, ischiendite, merendite, 

 etc., to indicate the segment on which they are borne) are of 

 considerable importance in the study of insectan anatomy, 

 since the galea, lacinia, and certain structures of the masti- 

 cating surface of the mandibles of insects are derived from these 

 endites of a crustacean limb, the coxendite, basendite, and 

 merendite (or the endites of the coxopodite, basipodite, and 

 meropodite) being the ones chiefly involved. 



The coxendite, or endite of the coxopodite (basal segment) of 

 the mouthpart-limb in other words, the homologue of the 

 structure labeled ce in Plate 8, Fig. 6, or in text figure 1 is 

 called the gnathobase by students of the trilobites and lower 

 Crustacea. This coxendite, or gnathobase, in the trilobites, 

 merostomes, and related forms, acts as a holding and commin- 

 uting structure (by abutting against its fellow borne on the 

 corresponding limb of the opposite side of the body) in manipu- 

 lating the food, and is the prototype of the masticatory portion 

 of the mandible of insects, as was pointed out in a previous 

 paper (Vol. 29, Jour. N. Y. Ent. Soc.). The coxendite, or 

 gnathobase, however, is not of any importance for the study of 

 the evolution of the maxilla, since it is the basendite and 

 ischiendite (or endites of the second and third segments of the 

 limb) which form the lacinia and galea of the maxilla, as will be 

 presently seen. 



In the trilobitan limb shown in Fig. 6 (Plate 8) the second, 

 third, and fourth segments of the limb bear endites (i. e. the 

 basendite, ischiendite, and merendite) labeled be, ie, and me, 

 and if the trilobitan limb were straightened up to assume the 

 position of the main axis of the crustacean limb shown in Fig. 

 8 of Mysis, it would be seen that the endites labeled be, ie, and 

 me in Fig. 8 correspond to the endites bearing these labels in 

 Fig. 6 (although the basal endite ce of Fig. 6 is not represented 

 in Fig. 8). The exopodite (ex of Fig. 8) has been omitted from 

 Fig. 6, since it would overlap and hide the endites, if drawn 

 in this view. 



If we compare Fig. 10 of a maxilliped of the crustacean 

 Gammarus, with Fig. 8 of a maxilliped of the crustacean Mysis, 

 it will be seen that the exopodite ex and epipodite ep of Fig. 8, 

 have been lost in Fig. 10, and instead of three endites be, ie and 

 me being present as in Figs. 8 and 6, only two of them be and ie 

 are retained in the maxilliped shown in Fig. 10. By comparing 

 the maxilliped of Gammarus (Fig. 10) with that of the other 

 crustacean shown in Fig. 8, there can be no doubt that it is the 

 endopodite en alone, and not the exopodite ex of Fig. 8, which is 

 retained in Fig. 10, and this fact is of the greatest importance in 



