88 PROTOPLASM OF PROTOZOA 



upon release of the pressure. Animals cut two-thirds across may keep 

 their shape; this argues for a stiff consistency of the ectoplasm, as well 

 as a tough pellicle. Any apparent modification in the shape of E. patella 

 occurs only from outside pressure, since the animal is unable to vary its 

 shape. Other hypotrichs may be similarly armored, as is shown by the 

 fact that they are broken in the ultracentrifuge (King and Beams, un- 

 published work) so that fragments are found swimming around as 

 though the whole animal were brittle rather than plastic. In other forms, 

 such as Paramecium, the body may be constricted when the animal 

 forces its way through obstacles. Upon ultracentrifuging in gum solutions 

 paramecia become much elongated and thin, because of the presence of 

 materials of different specific gravities in the cell. Such elongated animals 

 may survive and return to their normal shape unless the pellicle and 

 ectoplasm have been strained beyond the limit of their elasticity, in 

 which case the structure responsible for return to normal shape has been 

 destroyed and they die, permanently deformed (King and Beams, 1937) . 

 That the form of Paramecium is determined by the relatively firm outer 

 layers has been shown by some observations of Chambers (1924), who 

 tore the ectoplasm with a microneedle. The fluid interior pours out into 

 the surrounding water and the ectoplasm soon disintegrates; but oc- 

 casionally the fluid endoplasm forms a delicate surface film which main- 

 tains the integrity of the extruded mass. Merton (1928) has studied 

 these so-called autoplasmic paramecia which, deprived of pellicle, cilia, 

 trichocysts, and ectoplasm, take on the form of a fan-shaped amoeba, 

 which may live for some days, divide, and exhibit locomotor activities. 

 Under unfavorable conditions a rayed stage, with long pseudopodia-like 

 extensions reminiscent of a. A. radiosa, may be assumed. That the pellicle 

 is not the only element involved in rigidity has been shown for Blephar- 

 hma by Nadler (1929). The pellicle of this form may be shed after im- 

 mersion in weak solutions of strychnine sulphate. The "naked" animal 

 emerges from the old pellicle with the shape and elasticity characteristic 

 of the species. Eventually the pellicle is reformed, and the process may 

 then be repeated. 



That amoebae have elasticity of form to a considerable degree has 

 been shown by Jennings (1904), who bent a pseudopod with a glass 

 rod; when released the pseudopod sprang back into its original position. 

 Whole amoebae were also bent, with subsequent return to original form 



