INFUSORIA. 49 



to tlie stems of aquatic plants. The body in Vorticella forms 

 a kind of cup or " calyx " supported upon a long stalk, which 

 is in turn fixed to some solid object. The stem contains a 

 contractile fibre in its interior, and the animal can by this 

 means push itself out or coil itself up with the utmost rapidity. 

 The vibrating filaments or cilia are not scattered over the 

 whole surface of the bell-shaped bodj', but are collected to 

 form a kind of fringe or circle round the mouth of the calyx. 

 Nearly in the centre of this ring, or on one side, is placed the 

 aperture of the mouth, which leads by a short gullet straight 

 into the central soft sarcode of the interior of the body. A 

 nucleus and contractile vesicle are also present, so that in the 

 essential points of its anatomy Vorticella does not differ from 

 a free-swimming Infusorian such as Paramcecium. Indeed, a 

 transition between the two forms is found in the so-called 

 Trumpet animalcule or Stentor (Fig. 11, 5), which can detach 

 itself and swim about at will, at the same time that it is 

 ordinarily fixed by its thinner extremity to some solid object. 

 In Vaginicola (Fig. 11, a), again, we have an animalcule 

 closely related to Stentor, but having the body protected by a 

 horny or membranous sheath. 



All the Infttsoria we have been hitherto considering belong to a section 

 of the class in which the surface is furnished with more or less numerous 

 cilia. There are other forms, however, in which there are no cilia, but the 

 body is furnished with a number of radiating filauientous tubes, the extremi- 

 ties of which form little sucking-disks. Finally, there is another section in 

 which the organs of locomotion are in the form of long, contractile filaments, 

 termed " flagella," which may be combined with cilia, or may be the only 

 locomotive organs present. In accordance with these differences, the Infu- 

 soria are divided into the three orders of the Ciliaia, Suctoria, and FlageU 

 lata, of which the ciliated forms are by far the most numerous and most im- 

 portant. 



DisTEiBtJTiON OF Inpusohia in Space. — As regards the distribution of 

 Infusoria in space, there is little to say, except that they are of universal 

 occurrence in fresh water over the whole globe, and that they occur also in 

 the sea. In fact, the only conditions which appear to be necessary for their 

 existence are a certain quantity of water holding organic matter in solution. 

 Wherever these conditions are fulfilled. Infusoria are certain to make their 

 appearance. The attached forms of Infusoria, however (such as Vorticella, 

 Epislylis, Slentor, and others), do not appear to be ever developed in artifi- 

 cial infusions, and they are to be sought for on the stems of water-plants, 

 and in other similar localities. It seems hardly necessary to remark that, 

 as before defined, the occurrence of fossil Infusoria is not to be looked for, 

 as they possess no hard structures which are capable of permanent preser- 

 vation". It is only to be added in this connection that, if the animalcule 

 known as Noctiluca be rightly referred to this class, the Infusoria take a 

 very decided share In producing the diffused phosphorescence or luminosity 

 of the sea, which is occasionally such a beautiful spectacle even in our own 

 climate. 



