■11"2 Dr. A. Gruber's Contributions to the 



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 (flgs. 11 & 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 (u) also becomes quite 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 

 Amoeba diffiuens, one side of which is already quite liquefied, 

 while on the other half the double-contoured enveloping layer 

 is still retained, and on it even two pseudopodial cones, with 

 the processes issuing from them, are still visible. Fig. 15 is 

 also instructive in another way. There the cortical layer has 

 become fluid, and we see that tlie two pseudopodia wdiich have 

 persisted consist of the same hyaline protoplasm as the clear 

 border in which the cortical zone previously sharply separated 

 from it (see fig. 14) has dissolved itself. In the first state, 

 therefore, there would have been an envelope and an endo- 

 plasm enclosed by it, and from which the pseudopodia 

 proceeded, clearly distinguishable; in the latter both have 

 become fused into one. Kapidly as the broad, scarcely visible 

 border had formed, it can just as rapidly contract itself again ; 

 it shrinks to a certain extent together, until the narrow cortical 

 layer again originates from it. 



In this way Amwba diffliiens can continually change its aspect 

 completely in one or other of the modes described. Upon what 

 law this ])ower de])ends cannot be stated definitely ; very pro- 

 bably, however, difierent conditions of pressure come into play 

 in the matter. With a centripetal pressure acting uniformly 

 upon the whole periphery, the more fluid parts of the proto- 

 plasm are all pressed into the interior, and only the narrow 

 membranaceous boundary remains. This acquires a firmer 

 consistence by contact with the water ; and therefore at the 

 points where pseudopodia issue it is pushed aside by the 

 latter. If the general pressure ceases, the more fluid consti- 

 tuents again come forth from the interior, dissolve the solidified 

 cortical layer, and form the clear border. 



The best illustration of this explanation of the process is 

 furnished by those cases iu which a slow flowing forward of 



