202 Dr. L. Plate on the Genus Acinetoides. 



Figure 1 (PI. X., A) represents the larger of the two species, 

 which I venture to name Acinetoides Greeffii, in honour of 

 Prof. R. Greeif, to whom we are indebted for various valuable 

 investigations upon Protozoa. The animal attains a length of 

 0'046 millim. and an elevation of 0*02 millira. In form it 

 greatlj reminds us of the swarm-buds of many Acinetaj, for 

 example Dendrocometes paradoxus ^ St., but the arrangement 

 of the cilia is quite different. Acinetoides Oreeffii has a 

 plano-convex form. Seen from above or below (fig. 2) the 

 animal shows an elliptical outline ; the convex surface of our 

 Infusorian may be denominated the back, and the flat one 

 the belly. The latter is seldom quite plane, but generally 

 hollowed out like a basin, as sliown in fig. 1. Only one end 

 of it, which we shall regard as the anterior, usually makes an 

 exception to this, and projects beyond the ventral margin of 

 the body in the form of a low cone, bearing in its middle the 

 organ for the inception of nourishment, a sucking-thread 

 clubbed at the extremity, which may be traced far into the 

 interior of the cell-body and is distinguished only by its 

 remarkable shortness and rigidity from the similar organs of 

 most other Acinetas ; at least I have never found specimens 

 which had completely retracted their tentacle into the cell- 

 plasma ; but even in greatly disturbed animals this short 

 sucking-thread was always visible. Of the minute structure 

 of this organ I was unable to ascertain much, owing to the 

 want of high objectives ; it appeared to me to be a plasma- 

 rod traversed by a longitudinal canal. 



The persistent ciliation of the ventral surface is highly 

 characteristic of the genus Acinetoides. It does not extend 

 over the whole lower surface, but, as may be seen by an in- 

 spection of the ventral surface (fig. 2), only occupies an 

 elliptical inner area, leaving the whole peripheral border free 

 of cilia. The cilia are arranged in longitudinal rows, and 

 appear to stand in special grooves ; at least we observe upon 

 the ventral surface a delicate longitudinal striation which 

 extends over an area of exactly the same size as the cilia. 

 Each stria consists of granules lying one behind the other, 

 and thus produces about the same impression as the rows of 

 granules in Stetttor, between which the myophanic fibrils 

 take their course. I have been unable to detect in Acine- 

 toides any threads which might represent the latter, although 

 it is quite certain that the ventral surface of Acinetoides 

 Greeffii possesses a high degree of contractility ; I suppose 

 therefore that an examination by means of very powerful 

 objectives may reveal the presence of muscular fibrils in our 

 animal also. By means of this contractility it is able some- 



