304 ZOOLOGY SECT, vn 



ORDER 3. PLOIMA. 



Rotifera in which locomotion is performed by the ciliated disc 

 only. The tail is usually forked and more or less retractile. 



Sub-order a. Illoricata 



Plo'ima in which the trunk is not covered by a lorica. 

 Including Hydatina, Polyarthra, Asplanchna, etc. 



Sub-order b. Loricata 



Ploima in which a lorica is present. 

 Including Brachionus, Euchlanis, etc. 



ORDER 4. SCIRTOPODA. 



Rotifera provided with setose appendages moved by striped 

 muscles : skipping movements are performed by the aid of these 

 as well as swimming movements by the trochal disc. The tail is 

 either absent or is represented by a pair of ciliated processes. 



Including Pcdalion and Hexarthra. 



ORDER 5. TROCHOSPH^RIDA 



Globular Rotifera having the trochal disc represented by an equa- 

 torial circlet of cilia ; tail absent. 

 Including Trochospkwra only. 



Systematic Position of the Example. 



Brachionus rubens is one of several species of the genus 

 Brachionus : it belongs to the family Brachionidce, and to the 

 sub-order Loricata of the order Ploima. 



It is placed in the order Ploima in virtue of its active swimming 

 habits and the absence of looping or skipping movements. The 

 presence of a distinct lorica places it in the sub-order Loricata. 

 The family Brachionidse is distinguished by having a box-like 

 lorica open at both ends, and a long, flexible, retractile tail with 

 wrinkled surface and forceps-like termination. In the genus 

 Brachionus the lorica is not marked with ridges, and the tail is 

 very long and perfectly retractile. In B. rubens the anterior edge 

 of the lorica is produced dorsally into six spines and is sinuous 

 ventrally. 



3. GENERAL ORGANISATION. 



External Characters. The majority of the Rotifera are free- 

 swimming, being propelled rapidly through the water by the action 

 of the trochal disc. But in the Bdelloida (Fig 249, 5), in addition 

 to this mode of progression, the animal performs looping move- 

 ments like those of a leech : the tail in this order is freely jointed, 



