PROTOPLASM OF PROTOZOA 73 



that under conditions of low oxygen tension, Arcella releases its attach- 

 ment and floats to the surface. 



According to Chalkley (1935), locomotor activity and attachment to 

 the substratum are important factors in cytoplasmic fission in Amoeba. 

 If one of the daughter cells is detached while the other remains attached, 

 fission is not completed, but the unattached daughter flows back into the 

 attached. However, if both amoebae are detached, as in distilled water, 

 fission may be completed by the pushing of the pseudopodia of one ani- 

 mal against those of the other, thus breaking the narrow cytoplasmic 

 bridge between the daughter cells. 



In Testacea with lobose pseudopods, such as Dif^ugia and Centro- 

 pyxis, the organism is pulled along by means of contraction of pseudo- 

 pods, the tips of which have become attached to the substratum (Bellin- 

 ger, 1906). That this attachment is of special nature and of considerable 

 strength has been shown by Mast ( 1931a) , who prevented the shell from 

 being dragged along by the contraction of the pseudopods, under which 

 conditions the pseudopods were torn loose and snapped back toward the 

 shell. Testacea, such as Difjiugia, Lesquereusia and Pontigulasia, attach to 

 Spirogyra and devour the cell contents (Stump, 1935). According to 

 Penard (1902), the filose pseudopods of such forms as Pseudodifjiugia 

 and Cyphoderia have as their principle function the fastening of the ani- 

 mal to the substratum, to which they adhere with extraordinary tenacity. 

 Acanthocystis ludibunda (Helizoa) moves by adhesion of its axopods 

 to the substratum, after which they contract, rolling the animal along 

 over a distance twenty times its diameter in one minute (Penard, 1904) . 

 Schaeffer (1920) has estimated that the axopods of this form must ad- 

 here, contract so as to pull the animal along, and relax their hold, all in 

 the short time of two seconds. The reticulose pseudopods of the Forami- 

 niferan, Astrorhiza Umicola, attach and contract much as do the lobo- 

 podia of the Testacea. Here, however, the organism leaves a trail of 

 slime and bits of pseudopodia behind it, according to Schultz (1915). 

 In Grom'ia squamosa the reticulose pseudopods play a very slight part 

 in locomotion, but serve mainly as organs of attachment and food cap- 

 ture (Penard, 1902). 



The whole outer layer of many rhizopods is sticky: it is well known 

 that certain shelled rhizopods collect foreign particles to be included in 

 their tests. According to Stump (1936), Pontigulasia will not reproduce 



