270 PROTOPLASM 



not undertaken by any of the investigators whom we shall 

 shortly mention. The perfectly natural idea, that phenomena 

 of contraction were only conceivable in solid substances, was, to 

 a certain degree, the determining one in this conception ; it 

 was not, as a rule, definitely expressed — only in Eeinke (1881, 

 ii. p. 96) do I find a direct reference to it — yet this train 

 of reasoning at any rate formed the chief ground for con- 

 sidering the framework, conceived of as being solid or at least 

 very viscid, as the contractile substance. The following authors 

 professed themselves more or less definitely as being of the 

 opinion which has just been mentioned: Schleicher (1879), 

 Klein (1879), Eeinke and Rodewald (1881 and later), van 

 Beneden (1883 and later), List (1884), Carnoy (1884), Marshall 

 (1887), Fabre (1887), Ballowitz (1889), Boveri (1889), Rabl 

 (1889), and many others. 



In more recent times, as we have seen, some authors 

 even went so far as to ascribe the properties of muscle fibrils 

 to ordinary protoplasmic fibrils (see above, p. 260). 



{d) Objections to the Theory of Contractility 



Even at quite an early period strong objections have 

 been raised to the contractility theory, which were directed 

 just as much against the older conception of it as against 

 the turn which it took under the influence of the frame- 

 work theory. 



With regard to the movements of Amcebse and plasmodia; 

 Wallich (1863) had already drawn attention to the import- 

 ant fact, quite decisive as to the untenability of the con- 

 traction theory, that the commencement of a current does 

 not take place in the interior or at the hinder end of the 

 Amoeba, and then advance from this region towards the 

 portion of the surface that was streaming forwards, as would 

 be required by the contraction theory, but that, on the con- 

 trary, the current first makes its appearance in exactly the 

 opposite manner at the surface that was moving forwards, 

 and from thence gradually extends backwards. De Bary 

 (1864) also found this observation confirmed in plasmodia, 

 to this extent, that he certainly observed such currents, 

 which he termed centripetal ; but in addition, he believed 



