526 E. RAY LANKESTtlR. 



(preface to the English edition of (regenbaur's ' Comparative 

 Anatomy/ 1878) to indicate the group. The relationships of 

 the Arthropoda thus stated are shown in the subjoined table : 



{Sub-phylum 1. Rotifera. 

 „ 2. Cha^topoda. 



,, 3. Arthropoda. 



The Rotifera are characterised by the retention of what 

 appears in Molluscs and Chastopods as an embryonic organ, 

 the velum or ciliated prasoral girdle, as a locomotor and 

 food-seizing apparatus, and by the reduction of the muscular 

 parapodia to a rudimentary or non-existent condition in all 

 present surviving forms except Pedal ion. In many im- 

 portant respects they are degenerate — reduced both in size 

 and elaboration of structure. 



The Chastopoda are characterised by the possession of 

 horny epidermic chaetEe embedded in the integument and 

 moved by muscles. Probably the chaetfB preceded the 

 development of parapodia, and by their concentration, and 

 that of the muscular bundles connected Avith them at the 

 sides of each segment, led directly to the evolution of the 

 parapodia. The parapodia of Cha3topoda are never coated 

 vv^ith dense chitin, and are, therefore, never converted into 

 jaws; the primitive ''head-lobe" or prostomium persists, 

 and frequently carries eyes and sensory tentacles. Further, 

 in all members of the sub-phylum Chfetopoda the relative 

 position of the prostomium, mouth, and peristomium or first 

 ring of the body retains its primitive character. We do not 

 find in Chaetopoda that parapodia, belonging to primitively 

 post-oral rings or body-segments (called " somites," as 

 proposed by H. Milne-Ed wards j, pass in front of the mouth 

 by adaptational shifting of the oral aperture. (See, how- 

 ever, 8.) 



The Arthropoda might be better called the " Gnathopoda," 

 since their distinctive character is that one or more pairs of 

 appendages behind the mouth are densely chitinised and 

 turned (fellow to fellow on opposite sides) towards one 



