26 



THE ROTIFERA. 



I have named these orders as follows : 



I. EHIZOTA (the rooted). Fixed when adult. 

 II. BDELLOIDA (the leech -like). That swim with their ciliary wreath, and creep like a leech. 



III. PLOIMA (the sea- worthy). That only swim with their ciliary wreath. 



IV. SCIETOPODA (the skippers). That swim with their ciliary wreath, and skip with Arthropodous 



limbs. 



Now, the creatures contained in these orders, with a few exceptions, differ from each 

 other, first in their habits, and secondly in the following points : 

 I. In the structure of the foot. 

 II. In the arrangement of the ciliary wreath. 

 III. In the form of the trophi. 



I. In the structure of the foot. 



(1) The RMzotic foot is transversely wrinkled, and ends in a sort of sucking disk 

 (fig. 16) or cup (fig. 17). It is not retractile within the body, it never has telescopic 

 joints, nor is it ever furcate. 



Fig. 16. Hliizotic foot. Fig. 1 7. Rhizotic foot. 

 (FlosculaHd campanulaia.) (AMicerla ringetu) 



Fig. 18. Bdelloidic foot. 

 {Rotifer citrinus) 



Fig. 19. Scirtopodic foot. 

 (I'edalion mirum) 



(2) The Bdelloidic foot (fig. 18), on the contrary, is telescopic, retractile, furcate, and 

 is never transversely wrinkled, nor terminated by a sucking disk. 



(3) The Scirtopodic foot (fig. 19) is unique ; it is divided into two unconnected, 

 smooth, jointless styles, each ending in a ciliated expansion. 



(4) The Plo'imic foot is various in shape, but is always unlike that of any other 

 order ; for 



(a) if transversely wrinkled, it is yet retractile within the body, and almost invari- 



ably furcate ; 



(b) if jointed and furcate, it is not also telescopic ; 



(c) occasionally it is absent altogether. 



II. In the arrangement of the ciliary wreath. 1 

 (1) The Rhizotic ciliary wreath is of two forms : 



(a) The first encircles the body twice, by bending on itself; thus inclosing the 

 mouth, and having a dorsal gap between the points of flexure, figs. 20, 21. 



Fig. 20. RMzotic wreath (), front view. Fig. 21. Rhizotic wreath (), side view. 

 (Alelicerta ringens) (JJclicerta Hwjens) 



Fig. 22. Rhizotic wreath (&), 



seen from above. 

 (Flosculuria campanulata) 



1 In figs. 20 to 25, cio is the ciliary wreath ; pw is the principal wreath ; sio is the secondary wreath 

 bf the buccal funnel ; Ip the lips. 



