448 Dr. G. C. Wallich on Amoeba villosa 



slightest appreciable difference between the intimate texture 

 and composition of the two parts, the figure of their polygonal 

 cavities, the proportional thickness of the walls of the latter, 

 their optical characters, or the capability of the two portions to 

 coalesce*, — the fact being that each polygon is essentially com- 

 posed of both endosarc and ectosarc, the latter being the necessary 

 result of the contact of its internal surface with its fluid contents, 

 which do not consist principally of protoplasm, but of water; 

 whereas the former may be said to occupy the interval between 

 the wall of adjacent cavities, and is actually distinguishable 

 by its finely granular and viscid appearance wherever fusion 

 or coalescence has taken place to a certain extent. The pseudo- 

 podia and slightly thickened peripheral layer are also finely 

 granular. The former are given off from the external surface, it 

 is true; but, on the other hand, the walls of the polygonal 

 cavities present no appreciable differences in character from the 

 pseudopodia, beyond being flattened instead of filamentous ex- 

 pansions of the same tissue. And, lastly, I would lay special 

 stress on a phenomenon which this form of Actinophrys con- 

 stantly enables us to witness, namely, the absorption of the 

 vacuolar food-cavities, formed at the immediate surface of the 

 organism only at the period when required, and which are not 

 previously existing and persistent portions of the creature, as has 

 been supposed. As in Amoeba, the process of inception of food 

 consists simply in the formation of an extemporized cavity, 

 partly derived from the coalescence of the pseudopodia that have 

 captured the object, partly from the portion of ectosarc that 

 happens to be brought into contact with the object, and the 

 subsequent elimination of the nutrient matter by the vacuole 

 thus formed and now drawn into the centre of the body by 

 the inherent contractility of the surrounding protoplasm. If 

 this view of the phenomena be correct, we must either assume 

 that a constant diminution in bulk of the ectosarc must take 

 place at each formation of a food-vacuole, or admit what I con- 

 tend for, namely, that for every portion of the outer layer, con- 

 stituting the ectosarc for the time being, which is so removed 

 from its position, a portion of the subjacent endosarc forthwith 

 steps forward and fills up the vacant rank. As is well known, the 

 organism captured for food is sometimes almost as large as the 

 Actinophrys itself (see fig. 4) . Unless my hypothesis be admitted, 



* There appears no good ground for supposing that the vacuolation 

 witnessed in A. Eichornii is anything more than an extreme example of 

 what takes place frequently in Amoeba to a great, but not so great, an 

 extent. In Thalassicolla nucleata we have a near approach to the same 

 structure ; and, as in the form under notice, the larger vacuoles are ex- 

 ternal, the smaller ones internal, with reference to each other. 



