246 NATURAL HISTORY. 



they must bring water from without into the perivisceral cavity, and in the main trunks cilia are 

 seen moving with a flickering motion. 



A large single nervous ganglion is placed on one side of the body near the trochal disc, and 

 one or more eye-spots are placed upon it. Some Rotifers have a little sac tilled with calcareous matter 

 close to the ganglion, and it is probably a rudimentary organ of hearing. Moreover, a spur-like 

 ibrceps armed with setye is often, found projecting near the ganglion, and it may be a nervous organ. 

 The sexes are separate, and the ovarium and testis are simple glands which open into the cloaca 

 already mentioned. The eggs are laid and left, or in some they are attached to and carried about 

 by the female. In some Rotifera the eggs are of two kinds, and are termed summer and winter 

 eggs, the last being enclosed in a shell. 



In the sides of the body, beneath the skin and surrounding the perivisceral cavity, are muscular 

 fibres in bands; some pass longitudinally and others encircle the body, many being of striped fibre. 

 The jointed tail end is very telescopic in its movements in some Rotifera, and the terminating pincers 

 hold on to objects by their muscles. But in some Rotifera the later stage of life is not passed as a 

 freely- moving creature. Some form tubes to live in, and then their body ends in an adhesive disc. 

 However, the young of these, especially of the genus Lacinularia, enjoy a free-swimming life, and have 

 a circle of cilia around the large or mouth end of the body, and another circle around the tail end. 

 This immature Rotifer is analogous to the larvse of some of the worms already noticed, and as the adults 

 have perivisceral cavities, a pharyngeal armature and water systems, and are more or less segmented, 

 the necessity of classifying the Rotifera with the Vermes is evident. The trochal disc can be retracted 

 and everted in some Rotifers, and as soon as it is well out the cilia begin to move, lashing forcibly 

 in one direction, and producing by their general action whirlpools and currents in the water. They 

 have to do with the providing of food, with removing impure and giving pure water to the water 

 system, and also largely with locomotion, for when the foot is loosened, off starts the Rotifer, head 

 first, and it guides itself here and there with the hinder part of its body. The trochal disc varies 

 greatly in its construction, and forms a means of classification. Its margin may be continuous or 

 divided, there may be lobes to it resembling more than one disc, and it may be provided with long 

 tentacular processes. Finally, it may be used as a creeping organ, the Rotifer moving with its 

 head and tail, over substances, like a Leech. 



The Rotifera are found very universally in fresh, salt, and pure water, in pools, ponds, streams, 

 and gutters. They even manage to exist in moist earth, and some make homes of the open cells of 

 mosses and algae ; some are parasitic within other animals. They are tenacious of life, and will revive on 

 the application of moisture after they have dried up to a certain extent, but perfect desiccation is fatal. 

 Their shape differs considerably in the different genera into which the class may be divided ; some are 

 sac-shaped, others are vermiform; one group lead a social life, being attached by their long tail ends to 

 the number of forty or more. A fusiform shape is common, or that of an elongated cone. The 

 manner in which the trochal disc is retracted within the body and again put forth is as remarkable as 

 the similar process seen in some of the fixed Rotifers, whose delicate crown of long tentacles is unfolded 

 and protruded with great grace and perfectness. The activity of these interesting microscopic 

 animals is great under the stimulation of the sun and pure water containing minute animalculse 

 and vegetable organisms. They move and feed freely under such circumstances, directing themselves 

 here and there, choosing the best spots for feeding, and fix themselves so as to work their disc cilia to 

 advantage, or unfixing their forked tail, they move off by the same agency. 



The classification of the Rotifera is not in a satisfactory sbate, and whilst Ehrenberg arranged 

 them according to the peculiarities of their trochal discs, Dujardin classified them by their methods 

 of locomotion. There are some very curious forms which have not all the characters of the 

 Rotifera, and yet which have so many that they are allied to them, and this increases the difficulty. 

 Thus in the parasitic genus Albertia, which lives in the intestines of Slugs and Earth Worms, 

 and is -g^th to 7 yth of an inch long, the body is cylindrical, vermiform, rounded in front, with an 

 oblique orifice, around which there is a ciliated lip. There is a short conical tail, and the mastax is 

 rudimentary, there being only one or two forceps-shaped pieces which seize the food. 



A Rotifer of the genus Lindia* also has a vermiform body, rounded in front ; but it has no 



* Lindia '.orulosa. 



