392 GENERAL HISTORY OF THE INFUSORIA. 



Sect. IV.— OF THE ROTATORIA OR ROTIFERA. 

 (Plates XXXII.-XL.). 



General Characters. — Symmetrical animals, having a distinct head and 

 body ; the former sui-mounted by a wreath of cilia, the latter presenting 

 transverse folds or joints, with a simple alimentary canal and internal maxil- 

 lary apparatus ; a muscular and a water-vascular system ; nerves and nervous 

 ganglia, but not arranged in a symmetrical chain ; reproductive organs sepa- 

 rate in opposite sexes ; and propagation without imdergoing actual metamor- 

 phosis, by ova of two forms. The Rotatoria, moreover^ are destitute of limbs 

 in pairs, but have mostly the posterior extremity of the body produced as a 

 powerful, although a symmetrical, organ of locomotion, in which a transverse 

 articulation is particularly evident. 



This is a very natural gToup of animals, — its characters being definite, and 

 readily recognized by reason of the comparatively large size and transparency 

 of the organisms. The name Uotatoria, sometimes exchanged for Rotifer a, 

 is derived from the apparent whirling or wheel (rofa)-like motion of the 

 ciliary wreath aroimd the head, seen in most species. Since this rotary 

 movement is not universal, and at best but an ocular deception, some ob- 

 servers have been discontent with the appellations derived therefrom ; and 

 Dujardin, for one, has suggested as preferable the term * Sysiolides/ as 

 indicative of the remarkable contractile and flexible nature of their bodies. 

 They are also still spoken of imder the old name of ' wheel-animalcules ; ' 

 indeed, the early observers of the class actually believed the animals to be 

 furnished with wheels, by the rotation of which they moved. 



External Form, Integument, and Appendages. — The Rotifera are symme- 

 trical, and in this respect contrast with the asymmetrical Protozoa. They 

 present a determinable dorsal and abdominal surface, and consequently a right 

 and a left side. They have an oblong, ovoid, or much-elongated figure, and 

 are mostly separable, by the presence of a constriction more or less developed, 

 into an anterior segment or head, alid a larger posterior one or trunk. The 

 extension of the latter in a tail-like fashion may be regarded as a third seg- 

 ment. The constriction or narrower portion behind the head is frequently 

 called the neck ; this is wanting in many cases, and then the head is undistin- 

 guishable from the trunk as a distinct section, e. g. in Notommata Myrmeleo. 

 On the contraiy, the separation of the head from the trunk is weU seen in 

 Brachionus (XXXIX. 15-18; XL. 11), Steplianops (XL. 8-10), Euchlanh 

 (XXXIX. 4), Noteus (XXXVIII. 25), and Melicerta (XXXYIL 17). The 

 articulation of the tail-like segment is always evident. In a certain number 

 this prolongation is wanting ; and the animal is then tailless, — e. g. Anurcea 

 (XXXV. 495-498) and SaccuJus (XXXIX. 18). 



To facilitate the recognition of the general divisions of the body of Rotatoria, 

 considered as bilateral symmetrical animals, Mr. Gosse furnishes the following 

 remarks (Phil. Trans. 1855, p. 424) : — The bilateral organization is, he ob- 

 serves, in most cases " obvious, — the motions of the animal, like those of the 

 footed larvse of insects, being performed on the belly, with the head foremost. 

 Where this is not the case (as T\ith those genera which, either with or with- 



