68 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



chophorans in the Arthropoda. Though a modern onychophoran 

 shows no external segmentation of the body in the adult stage, the 

 segmented repetition of internal organs and the complete body seg- 

 mentation of the embryo leave no doubt that the Onychophora are 



Papd 



AlCnl DV 



\ / 



Papd 



Fig. 26. — Diagrammatic transverse sections of Nereus (A) and Peripatus 

 (B), showing comparative structure of the appendages of a polychaete annelid 

 and an onychophoran. 



AlCnl, alimentary canal ; Com, nerve commissure ; DDph, dorsal diaphragm ; 

 dm, dorsal muscles; DS, dorsal sinus; Dsp, dissepiment; DV , dorsal blood 

 vessel ; dwn, dorsoventral muscles ; NC, lateral nerve cord ; Nph, nephridium ; 

 Npr, nephropore; Papd, parapodium ; SlmGld, slime gland; vm, ventral muscles; 

 VNC, ventral nerve cord. 



fundamentally metameric animals. The body cavity is undivided by 

 dessepiments, the primitive coelom is represented only by the lumina 

 of the nephridia and the gonads, and the embrj^-ogeny of the Onycho- 

 phora gives the key to the early embryonic development of the arthro- 

 pods. The onychophoran legs have a lateroventral position on the 

 body (fig. 26 B) as in the arthropods, in contrast to the lateral posi- 



