OP ARTS AND SCIENCES: FEBRUARY 14, 1865. 399 



twist about each other in such a way as to resemble a sharply-pointed 

 screw, with a long drawn out double thread. Such is the condition in 

 which this pseudo-flagellum is most frequently seen, and then, with the 

 best magnifying powers, up to five hundred diameters, its compound 

 nature is not easily recognized. But there are times when the whole 

 group of cilia spreads out into a distinct brush, so that each individual 

 ciHum may be seen. The base {fi^) of attachment is in the axial 

 plane of the body, a short distance posterior to the mouth (w?), and 

 distinctly disconnected from it, as has been already noticed. When 

 not in motion, which seldom occurs, the brush lies along the median 

 furrow {mf) which trends from the mouth to the posterior end of the 

 animal, and in this position it projects for nearly half its length beyond 

 the body. Its most ostensible use would seem to be that of a sort of 

 rudder when the creature is swimming, and as a means of attachment 

 when not progressing. The body may be seen gyrating, and at the 

 same time revolving on its longitudinal axis, for long pei-iods around a 

 point to which the pseudo-flagellum is attached, and upon which it 

 turns like a pivot. It is most frequent that, during this act, a part of 

 the brush separates from the rest, and performs the office of an extra 

 propeller. When the animal is darting and spinning thi'ough the 

 water, this appendage projects obliquely from its point of attachment 

 (as in tig. 1), and always following, with the narrower end of the body, 

 in the rear, it seems pretty evidently to be the main agent in the vari- 

 ous and sudden tackings to which this infusorian is addicted, and also 

 the axis upon which the body revolves ; at least the latter whirls, re- 

 peatedly changing as quick as thought from right to left, or vice versa, 

 upon an imaginary axis which is oblique to its greatest length, and 

 which exactly corresponds to the trend of the flagelliform appendage 

 when operating in this capacity. Under these conditions the animal 

 shoots along with a compound motion, which might be described as 

 wabbling, or like the action of an eccentric wheel. Apparently in 

 confirmation of this view the annular, obliquely transverse anterior 

 {of) and posterior {pf) furrows trend almost exactly at right angles 

 to this imaginary axis. These two furrows seem, at first sight, to be 

 bands of vibratintj cilia, and in fact it is in the line of their trend that 

 these cilia are most readily detected, simply because they are rather 

 more crowded alons their edsres than elsewhere ; but an attentive ex- 

 amination reveals their presence all over the body, posterior to the 

 anterior transverse furrow. Between the two furrows (i. e. from of to 



