CHAPTER VIII. 



PHYLUM ROTIFERA.* 



Minute animals icith a ciliated trochal disc, an anterior mouth, 

 and a dorsal posterior anus. Perivisceral cavity well developed ; 

 excretory system ivith flame-cells ; vascular system absent. 



The Rotifera are small aquatic organisms which swim in the 

 water by means of a ciliary apparatus at the front end of the 

 body, called the trochal disc. This consists of the anterior end 

 which generally has a somewhat discoidal form, and of the cilia 

 which are disposed in one or two rows round its margin. The 

 name "Wheel-animalcules," sometimes applied to this group, is due 

 to the co-ordinated movement of these cilia, which produces the 

 appearance of a rotating wheel, or in some cases, when the ciliary 

 band is indented or interrupted at its median dorsal point and 

 its median ventral, of two Avheels (Philodina, Limnias). It will 

 be useful to use the word corona for the discoidal anterior end 

 of the body, and velum for the ciliary apparatus of its margin 

 the whole being the trochal disc. The posterior end of the body 

 tapers, and is called the foot or pseudopodium ; it may be jointed, 

 and the joints are often telescopically retractile. It terminates 

 either in a sucker-like surface for adhesion, on which the secretion 

 of a cenient-gland may be poured, or in two (or more) styles, which 

 can be used as pincers for anchoring the animal (Fig. 244). It 

 is used both for locomotion and attachment. 



The trochal disc is generally retractile, and the foot is, in rare 

 cases, absent. 



The mouth is on the ventral side of the trochal disc, and the 

 anus is on the dorsal surface, usually near the foot. 



* Ehrenberg, "Die Infusionsthierchen als vollkommene Organismen," Leipzig, 

 1838. C. T. Hudson and P. H. Gosse, ".The Rotifera or Wheel- animalcules," 

 2 vols., London, 1886. L. H. Plate, " Ub. d. Rotatorienfauna d. bottnischen 

 Meerbusens," etc., Z. f. w. Z., 49, 1890. C. Zelinka, "Studien lib. Rotatorien," 

 Z.f. w. Z., 44, 1886 ; 47, 1888 ; 53, 1892. 



