192 The Irish Naturalist. 



the "worms." Having thus placed our rotifer among its 

 relations, we will next proceed to describe its appearance. 



A denizen of the water, of microscopic size, it is barely to be 

 seen by the naked eye, as a tiny white speck moving about 

 against a dark background. The microscope reveals its typical 

 form as that of a short cylinder, of which the upper end — the 

 head — is furnivShed with a wreath of hairs, or cilia, which is kept 

 in constant motion, having just the appearance of a revolving 

 wheel (hence the name), and which serves a double purpose, 

 that of an aid to locomotion, and that of creating a vortex to en- 

 trap the necessary pabulum. Besides this wreath of hairs, the 

 head is also furnished, in the greater number of species, with 

 lateral ear-like and ciliated appendages which can be everted 

 or withdrawn at the will of the animal. The lower end 

 terminates in a foot of one or several joints, which at its ex- 

 tremity is either developed into a suctorial disc, or bears one or 

 more toes of a chitinous texture. The integument of the body 

 is either soft and flexible, or hardened into a glassy coat, 

 termed the " lorica," which is often developed into beautiful 

 and fantastic patterns. 



Tiny atom as it is, the creature possesses a comparatively high 

 organization. A large brain occupies the interior of the head, 

 and in connection with it are one or more eyes, sometimes of 

 a most brilliant red or rose-colour, their position and number 

 varying according to the vSpecies. It has jaws and teeth of 

 quite formidable proportions, and knows how to use them too ; 

 in some families these are formed for biting and cutting only, 

 in others they are modified into pounding and crushing 

 machines. The digestive system is simple and easily dis- 

 cerned ; it consists of a stomach, intestine, and gastric glands, 

 which latter are usually in the form of two clear globate bodies 

 seated on the fore-part of the stomach, at either side of the 

 oesophagus. The excretory system is represented by loose, 

 irregular, and sometimes branching tubes, which originate in 

 the head, descend to and terminate in a clear bladder-like 

 vesicle situated near the end of the body, which dilates and 

 contracts at regular intervals, and is termed the contractile 

 vesicle. There is a well-developed ovary, which lies along the 

 ventral floor, and usually one or two ova are to be seen in an 

 advanced stage of development. The muscles in some species 

 are very conspicuous, notably in Pleterodina, in which they are 



