92 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



(Heymons) and in the embryo of Carausius (Wiesmann). Postan- 

 tennae are commonly present in insect embryos, but their rudiments 

 persist in only one or two doubtful cases in the adult. The postantennal 

 appendages are the second antennae of Crustacea, and probably the 

 chelicerae of Arachnida and Xiphosura. Endites of their bases may 

 have been the functional jaws of the insectan and myriapodan an- 

 cestors in the protocephalic stage. 



11. The gnathal appendages have been derived from organs having 

 the structure of uniramous ambulatory legs. All the primitive ar- 

 thropod appendages were probably uniramous ambulatory limbs. Bira- 

 mous and natatory appendages are characteristic of the Crustacea only, 

 and are probably secondary adaptations to an aquatic life. 



12. The mandible is a common inheritance from an early ancestor 

 of the eugnathate group of arthropods. Its primitive structure re- 

 sembled that of the first maxilla of modern insects, and is best pre- 

 served in the Myriapoda. 



13. The diplopod mandible consists of a base subdivided into cardo 

 and stipes, bearing a large movable lacinia. but lacking a galea and a 

 palpus. In the typical chilopod mandible, the division between cardo 

 and stipes has been lost, and the lacinia is less free. The musculature 

 of the chilopod mandible is more primitive than that of the diplopod 

 mandible. In the crustaceans and insects the mandibular lacinia is 

 either lost, or is fused with the base to form a solid jaw. The mandib- 

 ular palpus is retained in many Crustacea. The mandible is repre- 

 sented by the pedipalp in Arachnida. 



14. The first maxillary appendage is best developed in the insects, 

 and probably here preserves the primitive structure of the mandible. 

 Its musculature is exactly duplicated in the musculature of the man- 

 dibles in the diplopods and chilopods. Neither the first nor the second 

 maxillae of the chilopods gives any evidence of ever having at- 

 tained the special structure of the primitive mandibles and the insect 

 maxillae. 



15. A primitive gnathal appendage had the structure of a gener- 

 alized ambulatory appendage, consisting of a liinh basis and a fclo- 

 poditc. The basis represents the coxa and subcoxa of a thoracic leg, 

 but its division into cardo and stipes is not a true segmentation. The 

 galea and lacinia are movable endites of the basis, with the origin 

 of their muscles in the stipital region of the latter. The telopodite 

 becomes the palpus of the gnathal appendage, and its basal articula- 

 tion is the homologue of the coxo-trochanteral joint in the leg. The 

 palpifer is not a segment of the limb, but a subdivision of the stipes 



