112 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



is similarly divided secondarily into two parts (cardo and stipes), 

 though it is not clear that the two parts exactly correspond with the 

 subcoxa and coxa of a thoracic leg. The palpi, however, are thus 

 seen to be the telopodites of the head appendages. If the interpretation 

 concerning the primary segmentation of a gnathal or a thoracic 

 appendage into basis and telopodite is now carried to the appendages 

 of the abdomen, the basal plates or basal lobes of the latter become 

 the true limb bases, and the telopodites should be freely movable ap- 

 pendicular processes of the bases. 



In general, then, it appears that the arthropod limb is divided by a 

 joint near its base into a proximal part, the primary limb basis, and 

 into a distal part, or telopodite. The baso-telopodite joint is the coxo- 

 trochanteral joint of a fully segmented limb, which is the joint be- 

 tween the coxopodite and the basipodite in terms usually employed 

 by carcinologists. The use of the term " basipodite " by Borner 

 (1904, 1921) to designate the subcoxo-coxal base of the limb creates 

 a duplication in nomenclature that is likely to be confusing. The 

 movement of the telopodite on the basis is typically in a vertical 

 plane, produced by levator and depressor muscles arising in the basis 

 (fig. 25 A, 0,Q). 



On the assumption that the basal mechanism of all the limbs is 

 fundamentally the same in all groups of arthropods, we can imagine 

 a simple primitive condition in the arthropodan ancestors in which 

 the entire series of appendages had a uniform line of flexure near 

 the body, along which the distal parts of the limbs, or telopodites, 

 were movable in a vertical plane on their bases. The bases, on the 

 other hand, turned forward and rearward on the axes of their attach- 

 ments on the body. Wherever the basis is differentiated into a coxa 

 and a subcoxa, the primitive basal movement of the appendage on the 

 body is lost, but is replaced by a vertical axis of promotion and remo- 

 tion between the subcoxa and the coxa, as the latter becomes sec- 

 ondarily the functional base of the limb. Finally, if the limb becomes 

 rudimentary and loses its basal musculature, the basis might become 

 transformed to a simple immovable lobe or plate of the wall of 

 the supporting body segment, with the telopodite reduced to an ap- 

 pendicular process movable by muscles arising in the basis. 



Other Theories on the Morphology of the Abdominal Appen- 

 dages. — The principal problem encountered in a study of the abdom- 

 inal appendages of insects is that of determining the homologies of the 

 parts of the appendages with those of a generalized limb. The basis, 

 the stylus, the gonapophysis, the eversible vesicle, each raise ques- 

 tions as to its nature and derivation. 



