Recent Researches on the Inftcsoria. 301 



a view which few adopted, from the difficulty of conceiving such a 

 mode of connexion to subsist between the parts of organized beings. 

 Nevertheless, the distinction which he was led by this view t« 

 establish between the motion in question, which he named Rota- 

 tion, and that of simple cilia which he called Vibration, has pre- 

 vailed till now, and the animals exhibiting these two mptions 

 have been distinguished from each other by the names of In- 

 fusoria Rotatoria, and Vibratoria. Dr Ehrenberg considers thait 

 there is no essential difference between the two motions, being 

 both, produced by cilia which move individually in the same 

 manner, but from their diflf'erent arrangement in the two cases 

 produce a different general effect. The apparent rotation or 

 turning round of the whole circle, is obviously an optical decep- 

 tion which he endeavours to explain thus : The ciha composing 

 the rotatory organ have the same structure, and move in the 

 same manner as the single cilia already mentioned, that is, they 

 are moved round. by minute muscles attached to their bulbous 

 roots, in such a way as at each revolution to circumscribe a co- 

 nical space. When viewed sideways in performing this revolu- 

 tion, they must necessarily pass at one moment a little nearer, at 

 another a little more distant, from the eye, or in other words, al- 

 ternately become more and less distinct to the view at very short 

 intervals, and this alternation occurring over the whole circle, 

 gives rise to a seeming change of place in every point of its cir- 

 cumference and a consequent appearance of rotation. Other ex- 

 planations of this singular phenomenon have been offered, of 

 ■which I may refer, on account of its ingenuity rather than its 

 probability, to that suggested by Dutrochet, in the Annales du 

 Micseum (THistoire Naturette, tom. xx. 



In regard to the use of these organs, Dr Ehrenberg observes, 

 that they are chiefly employed by the animals in catching their 

 food by the currents which they occasion, and in swimming ; 

 they therefore serve as organs of prehension and of locomotion. 

 He supposes also that the currents which they produce must be 

 subservient to the respiratory function, by constantly bringing 

 a new portion of water into contact with the surface of the ani- 

 mal, a supposition which appears to me highly probable, when 

 we compare these currents with those which I have elsewhere 

 shewn to take place along the surface of the respiratory organs 



