AND PHYSIOLOGY OF TRICHODINA. 121 



the row appears to terminate abruptly, and exactly at tbat point there seems to be the 

 end of a bristle, i. e., the tip of the latter ends just where the line of ciliary points termi- 

 nates, — the two are coincident! Sometimes the point of coincidence is seen opposite the 

 left side of the vestibular aperture, at other times opposite the middle of the same, or 

 considerably to the right of it. Again this point of coincidence appears to run rapidly 

 from left to right, and then back again from right to left, as if the tip of the bristle were 

 sweeping along the row of cilia, and pushing them back in succession. In addition to this 

 it will be noticed that the end of this false bristle varies in thickness from moment to 

 moment, during the shifting of the point of coincidence ; and finally it may be remarked 

 that it frequently seems to be broken into a series of dots, or short, irregular pieces. 

 This last feature gives the clue to the mystery. The apparently disjointed pieces 

 of the tip of the false bristle are nothing more nor less than the foreshortened points 

 of the closely approximated, successive cilia, as they project toward the eye clurino- 

 the descent of the row into the vestibule. The point of coincidence mentioned above 

 is the place where the row bends abruptly toward the aperture of the vestibule ; and 

 the shifting of this point is the changing of the trend of the ciliary tips. The line 

 of attachment of the cilia is not changeable, and it may be readily traced to the 

 bottom of the vestibule ; but the cilia whilst projecting, at various and constantly diver- 

 sified angles, from their base of attachment, are so disposed that their approximated tips 

 form a frequently varying, undulating line. The reason why the "bristle" sometimes unac- 

 countably disappears during observation, arises from the fact that the cilia have so changed 

 their position that they do not afford a view which presents the appearance of such a 

 body. Usually, however, the cilia are curved transversely to the axis of the vestibule, so 

 that they form as it were a cylinder of juxtaposed hoops or circles ; and it is not to be 

 wondered at, therefore, that in almost any position the outline of this cylinder should 

 appear as a single line, or filament. In a view directly into the aperture of the vestibule, 

 the bristle, so-called, is not to be seen, for the very reason that the cylinder is presented 

 endwise, and on this account, too, the vestibule appears to have a double contour, the inner 

 one of these contours being nothing less than the series of curved cilia placed closely side by 

 side, and trending transversely to the axis of the cavity in question. This is a particularly 

 facile observation in Vorticella, and none the less so in Carchesium. Finally, it may be said 

 on this point, — and coming last it is of no less importance than what has preceded, but on 

 the contrary is worthy of the utmost consideration in an optical point of view, — that 

 were the so-called bristle a genuine body, it would be in focus at only one particular 

 adjustment of the lens ; whereas we find, that, having obtained what appears to be a clear 

 and definite view of a filament, it does not go out of view by a change of the focus over a 

 considerable extent above or below that horizon. This, one may readily perceive, would 

 be the case in observing the outline of a transparent cylinder ; and as the closely approx- 

 imated, curved cilia form such a cylinder, the outline of the latter is likewise as variable as 

 that of any other similar form. 



§ 5. The Locomotive Organs. 



The locomotive organs are divided into three quite distinct sets, and appear to have as 

 many diverse offices. They are all situated at the extreme posterior end of the body. 

 Taken in their order, they stand thus : 1st, a veil, or membranous annular margin (/, f 1 ) ; 



JIEMOIRS BOST. SOC. NAT. HIST. Vol. I. 31 



