FINE STRUCTURE 37 



2. Holdfast 



A history of our knowledge of stentor's anchoring organ is given 

 in Andrews' (1945) most complete account of this organelle, which 

 confirmed and extended the early observations of Gruber (1878). 

 Stein (1876) thought that stentors fastened in part by means of a 

 tiny suction cup. This idea was revived by Dierks (1926a) who 

 described the myonemes as not continuing all the way to the 

 posterior pole but leaving the ectoplasm near the tail end to turn 

 inward toward the center of the cell where they took another bend 

 as they joined together to make a bundle pointing forward. The 

 result was a cone of contractile elements open toward the terminal 

 pole. Assuming that the recurved ends of the myonemes are 

 independently contractile while their anterior extensions remain 

 wholly relaxed, and that the posterior end of the animal could 

 somehow produce a tightly adhering cup, he conceived that this 

 arrangement produces a suction which is the principal means of 

 attachment. This scheme is highly dubitable. In the first place, 

 the study was made on killed and contracted animals, unattached. 

 Second, stentors can attach to the surface film where suction 

 should not be eflFective. Finally, among the other assumptions 

 mentioned, this conception was based on the questionable pre- 

 supposition that amoeboid processes with sticky substances could 

 not account for the firmness of adhesion which is observed. 

 Schroder (1907), however, also described myonemes as recurved 

 at the posterior end, but he did not advance the suction idea. 

 Instead, in the cone before-mentioned, he defined a special 

 cytoplasm from which the attaching organ was presumed to be 

 elaborated. I have sometimes observed the " hem " or sharp bend 

 in the cell contour toward the posterior end which Dierks des- 

 cribed as indicating where the myonemes turn inward but other- 

 wise found no confirming indications of his description in living 

 material. Whether Schroder's and Dierks' recurved myonemes 

 are artifacts of fixation can only be decided by successful preserva- 

 tion of animals in the fully extended^ state. 



Johnson (1893) figured the myonemes as running without 

 deviation to the posterior pole and hence his conception of attach- 

 ment was quite diff"erent. Body striping was described, however, 

 as not continuing all the way to the pole itself but stopping short 

 to leave a small terminal area which, because of its absence of 



