22 PROCEEDIISrGS OF THE ISTATIOlSrAL MUSEUM vol. 78 



given for a diagrammatic representation of the fundamental struc- 

 ture in the adult animal. The conditions may be presented schemat- 

 ically in the following way : 



Peripatus : A ys keaia : 



Frontal organ (embryonic). Frontal papilla. 



Antenna. Branched appendage. 



Jaw. 1st trunk leg. 



Slime papilla. 2nd trunk leg. 



1st trunk leg. 3rd trunk leg. 



Relationships to other forvis. — Aysheaia does not indicate any 

 relationship between the Arthropoda and Onychophora; it merely 

 indicates what was the general structure of the oldest members of 

 the latter group and emphasizes its isolation. The six setalike 

 claws alone serve to bring the Onychophora nearer to the existing 

 polychaets, and if the Onychaphora had a polychaet origin it must 

 have been in the very remote past from some extremely generalized 

 ancestor. It is clear that the general form of the group is not corre- 

 lated with terrestrial life. The recent discovery of Xenusion 

 auersioaldae Pompeckj in supposedly Algonkian rocks suggests that 

 segmented animals with annulated uniramous appendages at one 

 time played a large part in the earth's fauna. Heymons (1928), 

 indeed, in discussing Xenusion^ suggests that the modern Onycho- 

 phora, Tardigrada, and Pentastomida represent merely the relics 

 of an important palaeozoic assemblage of animals. Aysheaia gives 

 us some idea of the marine ancestors of one of the few surviving 

 members of that fauna. 



Systematic position. — It is becoming clear to most investigators 

 of the Arthropoda that the Onychophora, in spite of their tracheal 

 respiration and their reduced coelom and its corollaries, are mis- 

 placed in the Arthropoda. In Kiikenthal and Krumbach's Hand- 

 buch, the most authoritative survey of the Animal Kingdom yet 

 published, the Onychophora and Arthropoda are separated, and it 

 is probable that such a course will be adopted generally in the 

 future. The most rational course seems to be to follow Lankester 

 in the classification used in his Treatise (1900) and include the 

 arthropods and annelids in one phylum Appendiculata, or to revive 

 the old Cuvierian group Articulata as has been done by various 

 authors. 



The Arthropoda, Onychophora, and Annelida may then be con- 

 sidered as subphyla. Possibly this rank also should be given to 

 some of the " Stelenchopodous " groups and to Xenusion. For the 

 present purpose the following scheme may be adopted. 



