Natural History of the Vorticellge. 387 



tion in E. flavicans^ we find that this movement does not occur, 

 as at first sight appeared, in all parts of the interior of the 

 body. The entire conical hinder part of the hody, from the 

 attachment of the 'peduncle nearly to the point where the bellied 

 curve of the hell commences, takes no part in the movement 

 (PL XVI. fig. 1). This part also is not coloured, but hyaline, 

 and only occupied by a few dimly shining granules ; hence it 

 is strikingly differentiated from the coloured contents of the 

 bellied part of the bell (PI. XV. figs. 1 & 18). One sees most 

 clearly how the circulating mass of contents flows past the 

 inner wall of this conical hinder part without any portions of 

 tJie latter heing carried away hy the current. Evidently there 

 is here a fixed boundary between the constantly mobile fluid 

 contents and a firmer wall-parenchyma, which in the first 

 j)lace fills the whole conical base of the Vorticellan body, but 

 from this rises like a cup on the lateral walls and lines the 

 inner surface of the cutaneous covering above described, pre- 

 senting everywhere a sharp boundary to the fluid contents of 

 the body. 



Of this also we may convince ourselves by observation, by 

 carefully tracing the movement of rotation from the base 

 through the cavity of the bell. It is clear from this that there 

 can no longer be any question of a gradual transition of the 

 fluid body-contents into the firm parenchyma of the walls, of 

 an amalgamation of the whole into a common sarcode or pro- 

 toplasm filling the body as a parenchyma; for the rotation 

 becomes brisker and more regular the further out it is, and 

 passes everywhere ivith a sharp boundary by the iiiner walls of 

 the circumference of the body. If the contents gradually ac- 

 quired more consistence and tenacity outwards, and became 

 amalgamated here with the firmer cortical layer, which also, 

 although reluctantly, would be drawn into the rotation, the 

 movement must gradually diminish exteriorly. But precisely 

 the reverse takes place, as already remarked. Moreover, if the 

 cortical layer really rotated with the rest, how should we ex- 

 plain the fact that the contractile vesicle, the nucleus, the first 

 part of the nutritive tube (vestibulum and oesophagus), the 

 muscles, &c. are nevertheless still maintained in their definite 

 position ? Must not they also be carried away and thus conti- 

 nually change their position ? Or we must assume that these 

 organs are not situated in the cortical layer, but within the 

 cuticula. But they lie, as may be most easily ascertained, 

 beneath the cuticula and in the cortical layer, and are probably 

 not at all in contact with the former. In Rhizopoda, which 

 Stein adduces as objects of comparison and in support of his 

 view, and especially in Amoeba', such a difterentiation into a 



