NO. 6 INSECT ABDOMEN — SNODGRASS 65 



and. as above noted, a joint does occnr in the proximal part of 

 practically all fully-developed arthropod appendages that is evidently, 

 from its structure and musculature, to be identified as the joint be- 

 tween the primitive basis and the telopodite. This joint is the coxo- 

 trochanteral joint of an insect's leg. It is then reasonable to assume 

 that the same joint is retained in reduced appendages, and that, finally, 

 in an unsegmented limb rudiment it is the telopodite that has been 

 lost, and that the part which remains is the basis. 



The appendages of arthropods are prone to develop appendicular 

 processes on the limb segments. Such processes may be either cnd'itcs 

 or cxitcs, or both forms may occur on the same segment. Endites are 

 developed particularly on the basis, serving as masticatory lobes on 

 the gnathal appendages. In the Crustacea, exites of the basis are often 

 gill-bearing organs, and an exite of the proximal segment of the 

 telopodite commonly forms an outer branch of the appendage known 

 as the exopodite. The study of rudimentary appendages Ijecomes 

 complicated by the fact that it is often difficult or impossible to 

 determine whether a persisting part represents the main shaft of the 

 limb, or an appendicular process of the latter. 



BODY APPENDAGES OF CTIILOPODA 



The centipedes furnish a good example of arthropods that have 

 retained a long series of body appendages preserving the form and 



T 



Fig. 26. — Somewhat diagrainmatic cross section of a body segment of Litlio- 

 bius, showing the relation of the subcoxa (Sex) and coxa (C.v) to the body 

 and to the telopodite (Tlpd). 



function of ambulatory limbs. Each appendage of the pregenital re- 

 gion of the body is implanted in a membranous pleural area of its 

 supporting body segment between distinct tergal and sternal |)lates 

 (figs. 26, 27 A). The movable basal i)iece of a typical chilopod leg is 

 a small segment generally termed the coxa, or coxopodite (C.r). The 



