Recent Researches on the Ijifusoria. 299 



planted in the substance of the body by their base, which is not 

 jointed. They, therefore, never perform any rapid movements, 

 but they are capable of being slowly erected and depressed, and 

 seem to assist in the progressive motion of the animal, somewhat 

 in the same manner as the prickles of the sea-urchin. They are 

 found in but a few species. 8f/, The ci/ta, or hair-like organs : 

 these, either separate or combined together into a special appa- 

 ratus, form the principal instruments of motion in the infusoria. 

 By an attentive examination of the larger forms of them, Dr 

 Ehrenberg has discovered that they are furnished with a bulb at 

 the root, to which minute muscles are attached. A slight degree 

 of rotation impressed on the bulb causes a much more extensive 

 motion in the rest of the organ, which, in its revolution, is made 

 to describe a cone whose apex corresponds with the bulb. In the 

 Rotatoria, the cilia are always combined to form the compound 

 rotatory organs peculiar to that class, to be afterwards described. 

 In the Polygastrica, they are in a few instances entirely absent, 

 or at least not observable ; in other instances they are placed 

 round the mouth, or spread over the body generally, in which 

 case they are usually disposed in regular rows. Uncini, or 

 hooks, are setaceous appendages, curved at the point, which, 

 serve for seizing or clinging to surrounding objects. Stt^li, or 

 styles, are articulated at their base, and more moveable than the 

 setae or bristles ; they differ from cilia in being destitute of a 

 bulb, and in not performing a revolving motion. 



The compound organs of motion are found only in the Rotato- 

 ria, in which they constitute the very singular rotatory apparatus 

 peculiar to these animals which we have next to consider. The 

 structure of the simple cilia, and the mechanism and manner of 

 their movement, have been already described ; but in the ani- 

 mals of the class Rotatoria, the cilia are always combined to 

 form one or more organs of a more complex structure, which 

 are named the rotatory or wheel-like organs. Dr Eh/'enberg 

 has established the primary systematic divisions of that class of 

 infusoria on differences observed in these organs, of which he 

 reckons four different forms. In the most simple form the 

 cilia are disposed round the mouth in the figure of a horse shoe, 

 or of a circle interrupted at one part of its circumference, the 

 mouth occupying the interruption, and the cilia being not set in 



