38 THE BIOLOGY OF STENTOR 



Structure, he designated questionably as endoplasm. This would 

 correspond to the polar plasma later described by Schroder. Weisz, 

 too, (1948a) emphasized that the posterior end is clear and 

 structureless, but Dierks denied that there is any such '* naked 

 protoplasm ". Probably the pellucid polar endoplasm is responsible 

 for this illusion. Rather it would seem that granular stripes, ciliary 

 rows and myonemes cannot continue all the way to a fine point 

 without an improbable anastamosis of unlike elements and that 

 therefore at the posterior end the construction would not be strictly 

 closed but allow an opening for extrusions. 



The manner of attachment may vary with the nature of the 

 substratum. To clean glass, according to Johnson, terminal proto- 

 plasm adheres as a smooth disc ; against slime, pointed pseudopods 

 are given out from this disc ; and in attachment to the surface film 

 pseudopods become broad and branching as Andrews later des- 

 cribed more fully. Johnson also observed that stentors never attach 

 until stretched out and that the terminal cilia seem to feel about 

 for a place of attachment. 



Enlarging much on these observations, Andrews (1945) 

 described that in the outstretched stentor seeking attachment the 

 posterior cilia on the stalk come to a stop projecting outward while 

 the terminal ciUa, somewhat like the scopula of a vorticeUid, 

 remain active, possibly seeking a favorable spot or effecting a 

 preliminary attachment. By focusing downward on the foot of 

 stentors attaching to glass wool or a cover slip he was able to give 

 the most complete account of the holdfast, one which also has 

 interesting implications concerning the relationship between cilia 

 and pseudopodia. An amoeboid disc of naked cytoplasm is first 

 extruded from the posterior end to adhere by its stickiness, and 

 some of the posterior cilia are apparently transformed into viscid, 

 rigid, acicular pseudopods which he called " radiants". (If this 

 does indeed occur it carries the surprising imphcation, contradic- 

 tory to the hypothesis of the French school (see Lwoff, 1950) that 

 formed cilia can transform into something else without new 

 growth from a kinetosome specifically determined to produce such 

 a structure.) Meanwhile some of the terminal cilia remain active 

 ("undulants") but these gradually disappear with continued 

 attachment. Then the adjacent ectoplasm with its pigmented 

 stripes and ciliary rows is drawn out into extensive projections like 



