406 GENEEAL HISTORY OF THE mFUSORIA. 



anus always opens at the base of this segment, and on its posterior aspect ; 

 hence it is that, though often called a tail, it is really not homologous with 

 that appendage of higher animals ; and consequently most writers prefer to 

 name it pseudopodium, foot-process, or foot. It certainly has no evident re- 

 semblance to a foot, although anatomically it is a limb or member, and is 

 functionally an organ of locomotion and of support. It is much less con- 

 cerned with motion than the rotary organ, and, from its occasional absence, 

 is evidently a non-essential organ. A principal purpose which it seems to 

 answer is that of a rudder, steering the animal in its course like the tail of a 

 fish. However, occasionally, when developed in a styliform manner, as in 

 Scaridium (XXXIII. 423), it is a powerful and peculiar locomotive append- 

 age, enabling the animal to leap. The pincer-like termination seems to 

 enable the animals to hold fast to or grasj) objects, or to push themselves 

 forward. The short flexible toes developed on the pseudopodium, and the 

 supposed discoid extremities, serve to attach the animal w^hilst the head may 

 be moved fi^eely about, or whilst it advances in a leech-like manner by the 

 alternate forward movement of the head and foot. 



Of THE Muscular System ais-d Movements of the Rotatoria. Muscular 

 System. — In this class a muscular system, subservient to the functions of 

 locomotion, nutrition, &c., is well developed ; and, the integument being 

 transparent, its structure and arrangement are distinctly visible. The 

 muscles (XXXVI. 5 ; XXXVIII. 28 a) resemble fine lines, cords, or bands 

 passing from one part to the other, and may generally be distinguished by 

 being thickened during contraction, and attenuated by extension. All those 

 attached to the walls of the body arise from the inner layer of the integu- 

 ment, which is thickened at the spot. They may be considered, with refer- 

 ence to their functions, to be of two kinds — the one concerned in the general 

 movements of the body, the other in acting upon special organs or viscera. 

 The first constitute two sets — the one annular, encompassing the body, the 

 other longitudinal. The annular or transverse muscles (XXXIII. 5, 6 t; 

 XXXVIII. 26 v) are separated from each other by considerable intervals ; 

 and to them is due, in many species, the apparent segmentation of the trunk. 

 They are, so to speak, imbedded in the inner epidermic layer. Ehrenberg 

 mistook them for vessels. 



The longitudinal muscles are more numerous and definite (XXXVI. 51,91; 

 XXXVIII. 28 a ; XL. Im). Mr. Williamson believes that delicate fibres occur 

 in the thickness of the skin of the trunk, designed to shorten the animals by 

 corrugating the suiface. The long muscles extending from the posterior ex- 

 tremity of the body to the rotary organ and the maxillaiy bulb, and serving 

 to retract those parts, are the most highly developed. Dr. Dobie describes 

 muscular bands in Floscularia, passing up between the lobes of the ciliated 

 head, and more delicate fibres along the centre of each lobe towards its ex- 

 tremity. The muscles of the tail (foot-process) are also numerous, large, 

 and strong, and traceable to its terminal segments (XXXVI. 5 b ; XXXVIII. 

 26 n) on the one side, and on the other as far forward as the anterior part 

 of the body and the maxillary bulb. Williamson states that the fibres 

 reaching the extremity of the foot-process are inserted into a little concavo- 

 convex body found there. By its muscular apparatus the tail can be curved, 

 moved from side to side, and shortened, and in a few examples, e. g. Scaridium^ 

 doubled beneath the belly. The counterforce, whereby the pseudopodium 

 recovers its straight figure and position relative to the body, is the elasticity 

 of the integument. Where the sliding joints exist, this elasticity must 

 chiefly reside at the lines of junction, since ihe segments themselves have 

 great rigidity, and do not admit of corrugation. However, the extension of this 



