248 



GENEKAL HISTORY OF THE INFUSORIA. 



Concerning the mode of entrance of the nutritive matter when di'awn to the 

 surface, some difference of opinion prevails among the several writers who 

 have treated of it. Ehrenberg, true to his hypothesis, attributed to Actino- 

 phri/ina a mouth sui^mounted by a proboscis, and an anus at the opposite side 

 Avith an intercommunicating intestine and numerous stomach-sacs opening 

 into it. In short, they were, according to his scheme of organization, 

 Enantiotreta, of the class Enterodela. Dujardin rejected this account, and 

 supposed them to be nomished by absorption, carried on by the general 

 siuface, or by means of thick expansions from it. At the present time all 

 observers unite in denying a mouth, anus, and alimentary canal to Actino- 

 phryina, and in admitting that food may be introduced, and its debris dis- 

 charged, at any part of the smf ace, — a fact patent to direct observation, which 

 shows the seizing and the entrance of prey going on, occasionally, at more 

 than one point at a time (XXIII. 29-32). We have followed the captured 

 morsel until it apjDroaches the sui'face, and when the force of the tentacles 

 behind it still tends to press it onwards into the body. The following pro- 

 ceeding, according to Kolliker {op. cit. p. 28), now takes place : — " The spot 

 of the sui'face, upon which the captured animalcule is lying, slowly retracts 

 and forms at first a shallow depression, gradually becoming deeper and deeper, 

 in which the prey, apparently adherent to the surface and following it in its 

 retraction, is finally lodged (XXIII. 29 m). The depression, by the continued 

 retraction of the substance, now becomes deeper ; the imprisoned animalcule, 

 which up to this time had projected from the surface of the ActinophrySy 

 disappears entirely Avithin it ; and at the same time the tentacles, which had 

 remained with their extremities applied to each other, again erect themselves 

 and stretch out as before. Finally, the depression acquii'es a flask-like form, 

 by the di^awing in of its margin, the edges of which coalesce ; and thus a 

 cavity closed on all sides is formed, in which the prey is lodged. In this 

 situation it remains for a longer or shorter time, gradually, however, ap- 

 proaching the central or nuclear portion, and at last passing entirely into it 

 in order to await its final destination. In the meanwhile the external por- 

 tion of the Actinophrys regains in all respects its pristine condition. The 

 engulfed portion is gradually digested and dissolved." Whilst admitting 

 the general correctness of this account by Kolliker of the act of inglutition, 

 Stein asserts that, prior to the appearance of the prey in a depression of the 

 body, a large vacuole, rising above the smface, comes into contact with it, and 

 then, by its collapse, drags it downwards into the substance of the animalcule. 

 This stage he supposed KoUiker to have overlooked. However, Claparede 

 denies that the reception of food is ever effected by means of the expansion 

 and contraction of a vesicle, or that, as Kollilier believed, the food penetrates 

 the substance of the body by the force exercised upon it behind by the 

 tentacula : it is rather, he says, the substance of the body which approaches 

 and embraces the food ; for before the latter has touched the surface of the 

 body, it is seen to be envelojDed in a kind of mucus. -' This mucus is com- 

 pletely undistinguishable from the parenchyma of the Actinoplirys ; it appears 

 as though the substance of which it is composed had suddenly drawn itself 

 over the captured object. The elevation thus produced then slowly flattens; 

 and by this means the food is gradually di^awn into the body. Astasice, which 

 I frequently saw sucked in by Actinophrys in this way, continued to move 

 for a Httle time, endeavouring to break thi-ough the substance that enveloped 

 them ; their movements, however, soon ceased ; they became converted into 

 a globular mass, which circulated very slowly through the parenchyma with 

 the so-called vacuola." . . . . " At fii'st I thought the substance, which so 

 suddenly enveloped the object to be swallowed, was produced by the mere 



