ROTATORIA. 203 



[DUJARDIN (Infus. p. 268, 1841) gave reasons for the exclusion of 

 Chcetonotus and Ichthydium from the JKotatoria, and placed them 

 provisionally in his order Infusoires symetriques. Afterwards 

 C. YOGT referred them to the Turbellaria. SCHTILTZE discovered in 

 the sea-sand at Cuxhaven (1853) a new genus and species closely 

 allied in anatomical structure to our Ichthydina, which he named 

 Turbanella hyalina. Neither in Ichthydium nor Chcetonotus do the 

 cilia form a true wheel-organ round the mouth capable of protrusion 

 and retraction. In Ichthydium they are spread over the entire 

 abdominal surface ; in Chcetonotus over the whole of the anterior half 

 of the abdomen, and at the margin of the posterior half form a band 

 which surrounds the closely set, stiff hairs, which are much finer than 

 the spines on the dorsal surface and directed backwards to cover the 

 non- ciliated portion of the abdomen. The tail is forked, but not 

 jointed. The intestine is straight, the anal opening at the fork of 

 the tail. Neither vessels, nerves, nor muscles can be seen, except 

 that the oesophagus is muscular. The sexual organs are situated 

 between the intestinal canal and the integument of the back, the 

 testes consisting of a loose cluster of vesicles in front of the ovary. 

 SCHULTZE concludes that the Ichthydina of EHRENBERG (exclusive of 

 his genera Ptygura and G-lenophora which are true rotatories) must 

 be excluded from the Rotatoria, and that they belong more nearly 

 to the Turbellaria than to any other order of worms. There are 

 however remarkable differences of structure between them and 

 any family of Turbellaria. For in those Turbellaria which have a 

 straight intestine with anal opening, the sexes are distinct j whilst 

 in those which are hermaphrodite the intestine has no anal opening. 

 SCHULTZE contends however that in worms the characteristic derived 

 from the form of the intestinal canal is of greater systematic value 

 than that derived from the formation of the sexual organs : and 

 recommends that the Ichthydina, limited as above, be placed pro- 

 visionally amongst the Microstoma of the order Turbellaria, which 

 will then require to be subdivided into the dio3cious and the monoe- 

 cious (Ichthydina). See SCHULTZE in MUELLER'S Archiv. 1853. 

 s. 241-253. Taf. vi.] 



B. Rotatory organ multilobed or parted (Hydatincea EHRENB.) 



Otoglena EHRENB. Maxillse none. Ocelliform points three, the 

 middle one sessile, the two lateral pediculate. 



Enteroplea EHRENB. Body oval, oblong, anteriorly truncate. 

 Maxillaa none. Ocelliform points none. 



