296 PROTOPLASM 



Finally it is known that many Amoebae can to some 

 extent send out their pseudopodia free into the water, so that 

 Berthold sees himself constrained, in the case of the forma- 

 tion of pseudopodia of this kind, which in other respects is 

 precisely similar to that of creeping pseudopodia, to accept 

 the old theory of the pressure brought about from behind by 

 local contractions, and thus to assume two entirely different 

 causes at the same time in order to explain amoeboid move- 

 ment. 



Berthold finds a proof of the correctness of his hypo- 

 thesis with regard to amoeboid movement in the well-known 

 phenomena of movement shown by drops of water ad- 

 hering to a glass plate, if some ether or alcohol is brought 

 near them at their edges. As is well known, the drops 

 retreat from the ether or alcohol. Berthold thinks that 

 this phenomenon is to be explained in exactly the same 

 way as he supposed amoeboid movement to be, that is 

 to say, by the marginal angle of the drops becoming 

 increased on the side towards the alcohol, since the sur- 

 face tension is greater between water mixed with alcohol, 

 and glass, or rather its adhesion is less; and he believes, 

 as has been said, that the conditions are the same as 

 in the Amoeba, for which he postulates, in like manner, polar 

 differences of adhesion, i.e. a preponderance of adhesion 

 at the pole which is advancing forwards. Now, in the 

 first place, I regard the explanation given by Berthold of 

 the drop of water retreating from alcohol, etc., as only 

 partially correct. Its edge shrinks back on the approxima- 

 tion of the alcohol with an increase of the marginal angle, 

 and this may rightly be referred to the cause alleged by 

 Berthold. But with this shrinkage the movement would be 

 exhausted, and a continuous retreating movement, or, in other 

 words, a spreading out of the edge turned away from the 

 alcohol, would not be intelligible, since, after a corresponding 



specimens in a watch-glass, it is easily proved by slightly inclining the glass 

 that they do not adhere to it. On the slide it is possible to displace an 

 actively-streaming Pelomyxa by means of a light touch with a fine glass 

 rod. Only the hinder end, which in Pelomyxa, as in other Amoebae, is dis- 

 tinguished by special peculiarities, sometimes adheres to a slight extent. 



