PROTOPLASM OF PROTOZOA 89 



after release; Dellinger (1906) and Hyman (1917) have repeated these 

 experiments, as indeed may be done by anyone. Rowland (1924c) has 

 stretched the outer layer of A. verrucosa with microneedles; upon re- 

 lease the animal recovers its normal shape, apparently unharmed. The 

 protoplasm of plasmodia of slime molds (Seifriz, 1928) is at times 

 poorly elastic, and at other times it may be stretched into very fine, long 

 threads which snap back a goodly distance when released. 



Seifriz has also determined elastic values by inserting minute nickel 

 particles into the protoplasm of slime molds and attracting these particles 

 electromagnetically. On release of the current the metal particles return 

 to their original position; the distance traveled is measured and used as 

 an indicator of elasticity. A maximum stretching value of 4.4 microns 

 was obtained for liquid, previously streaming protoplasm of myxomy- 

 cetes, a maximum value of 292 microns for quiescent, highly viscous 

 exuded masses of protoplasm from plasmodia. This latter value is slightly 

 greater than that for gelatin solutions and slightly greater than that of 

 fresh egg albumen. 



The long thread-like pseudopodia of Foraminifera, which usually pull 

 the organism along by adhering to the surface terminally and then con- 

 tracting, have been shown to be elastic by Schultz (1915), who cut 

 these and observed them to snap back like a rubber band. 



The reticulose pseudopodia (myxopodia) of the Foraminifera are very 

 different from the lobose and filose forms in other Rhizopoda. The 

 former have a soft miscible outer protoplasm which leads to fusion on 

 contact with one another and a relatively rigid inner axial structure 

 which shortens without wrinkling when the pseudopod is withdrawn. 

 As this denser core is formed as an elongation "in the direction of 

 growth, strains will be set up during the process which will give rise 

 to ordered and preferential arrangement tending toward the crystalline 

 state" (Ewles and Speakman, 1930). Thus it will be seen that the axial 

 solid protoplasm of these myxopodia, although it is not in the form of 

 a fiber, serves the same function as the axial filament of the Heliozoa 

 and Radiolaria. 



Up to this point elasticity has been considered principally in connec- 

 tion with the protoplasm itself, or in its temporary completely reversible 

 structures. There remain for consideration those differentiations which 

 last the whole life of the organism and are usually irreversible, such as 



