516 Robert Hartmann: 



therefore analogous to the muscular lobes of Hydatina senta. 

 No structure, however, could be detected in these, nor in any 

 other part of the body beyond a mere granulär parenchyma. 



Fig. 22. ünder tbis power the whole character of the 

 ciliary motion is changed, and it is seen that what before ap- 

 peared to be a Single cilium is in fact a wave of cilia, and 

 that their motion instead of being in the direction of the cir- 

 cumference of the diso, is at right angles to this. The ciliary 

 phenomena are the most readily observed when the geramule 

 is nearly at rest, or has become langiiid; it then lies either 

 with the convex or the plane side uppermost, and with the 

 cilia, which are of great length, doubles in the middle them- 

 selves (Fig. 21), so that their extremities are brought back 

 nearly to tonch the niargin of the diso from which they arise. 

 The whole fringe of cilia is then suddenly unfolded, and after 

 waving up and down with a fanning motion they are either 

 again folded up towards the under surface of the body, or they 

 conamence their peculiar action. As the cilia have the ap- 

 pearence of moving in waves round the disc (Fig. 22), each 

 wave may be thus analysed. From a dozen to twenty cilia 

 are concerned in the production ef each apparent wave, the 

 highest point of which is formed by a cilium extended to its 

 füll length, and the lowest point between every two waves by 

 one folded down completely upon itself, the intervening space 

 being completed by others in every degree of extension, so as 

 to present something of the outline of a cone. (And it is remar- 

 kable that one of these corresponds very nearly in breadth with 

 oue of the supposed muscular lobes). As, however, the per- 

 sistence of each cilium in any one of these positions is only of 

 the shortest possible duration, a. each takes up in regulär suc- 

 cession the action of the adjoining one, so that cilium, which 

 by being completely folded up formed the lowest point between 

 any two waves, now in its turn by its complete extension forms 

 the highest point of a wave, and thus while the cilia are alter- 

 uately bending and unbending themselves, each in regulär suc- 

 cession after the other, the waves only travel ouward, whilst 

 Ihe cilia never change their positiou in this direction, liaving iu 



