INTRODUCTION. 1 1 



fantastic as they were varied. " Contractile fibres " 

 served for a time to explain the phenomena of motion. 

 Gruber advanced the theory of " pressure from behind." 

 There was, he held, a push forward of the more fluid 

 contents by the posterior ectoplasm, after the extrac- 

 tion of water had given the latter a tougher consis- 

 tency. The posterior extremity was " drawn into 

 threads as the Amwlxi advances, and the effect of a 

 reversal of the direction of movement, he said, was seen 

 in a flow of ectoplasm from the posterior region, the 

 more tenacious protoplasm appearing then on the oppo- 

 site side.* 



Dr. Wallich disputed Gruber 's theory, and reiterated 

 a view which he had long previously expressed, namely, 



FIG. 4. Anastomosing pseudopodia of Biomyxa vagans. x about 150. 



that the rush of granules is not dependent upon any 

 previous contractile effort exercised in the posterior 

 region. The flow merely takes the place of the ectosarc 

 which has been suddenly projected forward. Hence, he 

 argued, the motion is dependent on the contractile power 

 of " the external sarcode layer, and the endosarc only 

 passively participates in it." t 



Calkins sums up the controversy by remarking that 

 of late years, especially since 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 movements of amoeboid bodies 

 through the physical laws of liquids, and in particular 

 the laws of surface-tension. The origin of a pseudo- 



* ' Zeitschr. fiir Wiss. Zool.,' xl (1884). 



t ' Ann. and Mag. Nat. Hist.' (5) xvi (1885), p. 215. 



