84 THE PROTOZOA 



rest, Engelmann assumed, each inotogma has an elongated form, 

 becoming spherical upon contraction. If all contract at the same 

 time, as upon a sudden shock, the animal assumes a spherical con- 

 dition ; if the inotogmata contract in certain groups, a pseudopodium 

 is started, although some pseudopodia, notably the fine, thread-like 

 forms, are due to " relaxation " of rows of contracted units. A 

 considerable uncertainty is attached to Engelmann's theory, especially 

 when the attempt is made to explain special cases, and Butschli ('92) 

 shows in a very convincing manner that it does not justify the expec- 

 tations of its originator. 1 



Wallich ('63) early observed that the current in a progressive 

 pseudopodium does not begin in the body of the Amceba, but at the 

 periphery, an observation which de Bary ('64) confirmed in Mycetozoa. 

 Biitschli ('73) drew attention to the same fact soon after, and upon 

 the strength of .his observations appeared, even at this early period, 

 as an opponent of the contractility hypothesis. 



As stated previously, Butschli holds that protoplasm is essentially 

 a mixture of liquids consisting of a fluid alveolar' substance and an 

 intra-alveolar fluid of different physical nature. According to this 

 conception, which is widely accepted, a naked protoplasmic mass such 

 as Amceba must be subject to the same physical laws-as other fluids. 

 The rounding-out of drops of exuded protoplasm was early interpreted 

 by Hofmeister ('67), and by Engelmann ('69) before he adopted the 

 theory of inotogmata, as the same phenomenon that causes the 

 rounding-out of any liquid substance, i.e. to surface tension. Of late 

 years, especially since the appearance of Biitschli's masterly work on 

 the structure of protoplasm, there has been a general tendency to 

 abandon the older theory of contractility and to explain the move- 

 ments of amoeboid bodies through the physical laws of liquids, and in 

 particular, by the laws of surface tension. Weber ('55) compared the 

 protoplasmic movements in plant-cells to the streaming, due to surface 

 tension, in drops of liquid, and subsequently Berthold ('86), Butschli 

 ('92), Rhumbler ('98), and others, following the same line of investi- 

 gation, have obtained fruitful results. An excellent account of the 

 several interpretations along this line of reasoning may be seen in 

 Biitschli's Protoplasma? and it will be sufficient here to give the 

 most recent explanation as worked out by Rhumbler ('98) upon 

 the basis of Butschli's earlier view. Butschli says : " The expla- 

 nation of the processes of movement in Amceba is to be found, 

 therefore, to my mind, in correspondence with the interpretation of 

 the phenomena of streaming movements in the drops of foam, in the 

 fact that, by the bursting of some of the superficial alveoli, enchylema 



1 Cf. Butschli, p. 275. 2 pp. 172-212. 



