ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 211 



Of a nucleus nothing is to be seen in the resting state when the 

 folds obstruct the view of the interior. But if the Rbizopocl begins 

 to move when the body flattens, the nucleus becomes distinctly visible 

 (n in the figures), as a little disk surrounded by a narrow border, as 

 in most Amoebae. No contractile vacuole is present, a new proof of 

 the still unexplained fact that this structure is wanting in the marine 

 Rhizopoda. 



2. Amoeba adinopJiora Auerbach is very small, measuring 0'03- 

 0-04 mm., occurring pretty plentifully in all sorts of receptacles of 

 water in the neighbourhood of Lindaii. It is exceedingly suitable 

 for the completion and elucidation of the previous observations. 



The first striking point is, that here also the protoplasm is 

 distinctly surrounded by a double contour, the animal appearing as if 

 covered by an envelope. The periphery is for the most part perfectly 

 smooth, and only at one point does the animal extend a larger or 

 smaller number of lobate pseudopodia. In this way the Amoeba 

 acquires delusively the appearance of a thalamophorous Rhizopod 

 with a closely fitting thin carapace, from the orifice of which pro- 

 cesses protrude (see Fig. 9). In this condition the protoplasm in 

 the interior forms a tolerably compact mass, in which there are a 

 number of rather strongly refractive granules. 



When the number of the pseudopodia is large, so that a whole 

 tuft of them protrudes at once (Fig. 9), we see nothing of the cortical 

 zone at their place of issue. It is otherwise when only two or three 

 processes are pushed forth. The relations of the marginal layer 

 are then quite distinctly visible, and we find that, just as in 

 A. tentaculata, the cortex is pushed out into a cone at the apex of 

 which the pseudopodium makes its way out. Here, therefore, the 

 double contour is also produced by a more tenacious layer surround- 

 ing the animal, which must be penetrated by the protoplasmic 

 processes before they can issue (Fig. 14). Even in the previously 

 described form, however, we saw that we have not to do with a per- 

 sistent membranous structure, but that during the flow of the animal 

 the cortical layer becomes amalgamated with the rest of the sarcode. 

 This is much more distinctly observable in A. acfmophora. Thus 

 all at once we see how, as the animal changes its form, the pseudo- 

 podia are at the same time nearly all retracted, the body becomes 

 flattened, the cortical zone vanishes, and flows into a broad border of 

 clear protoplasm, which surrounds the darker richly granular mass 

 in the centre of the animal (Figs. 11 and 12 h). The latter often 

 remains for some time sharply discriminated from the hyaline border 

 (Fig. 17), but the boundary is soon obliterated, exactly as during 

 the formation of an ordinary pseudopodium (Fig. 12). In this state 

 the nucleus (n) also becomes distinctly visible, agreeing precisely in 

 its structure with those of other Amoebce. 



The melting of the fine cortical layer into the broad clear border 

 does not take place with equal rapidity at all points, so that a part 

 of the Amoeba often appears sharply limited, whilst another is already 

 surrounded by the clear space (Fig. 11 r, s). In Fig. 14, for example, 

 is represented an A, diffluens, one side of which is already quite 



P 2 



