RHIZOPODS, ACTINOPODS, SLIME MOLDS, SPOROZOA 75 



interest because of the perennial problem of ameboid locomotion 

 and its importance in the general question of protoplasmic 

 movement and sol-gel transformations. A digression to consider 

 this problem seems in order. The predominant theory of recent 

 years, in essential agreement with Mast's proposals of 35 years 

 ago (see, for example, Noland, 1957; Landau, 1959) holds that 

 forward flow of solated endoplasm results from contraction of 

 plasmagel in the posterior end of the moving cell. Fluid proto- 

 plasm reaching the tip of an advancing pseudopodium undergoes 

 gelation at its periphery to form a plasmagel sleeve. Contraction 

 of the gel in the posterior zone is followed immediately by 

 solation, thus replenishing the internal plasmasol. According to 

 Allen and co-workers (Allen and Roslansky, 1959; Allen, 1960, 

 1961; Allen, Cooledge, and Hall, 1960; Griffin and Allen, 1960), 

 this theory is too simple. They find that the endoplasm is not 

 uniformly solated and that hydrostatic pressure exerted by 

 posterior gel contraction does not suffice to explain forward flow 

 in such a non-Newtonian fluid. An axial core of endoplasm exhibits 

 a viscosity nearly equal to that of the gelated ectoplasm. The 

 authors postulate that streams or strands of cytoplasm move 

 forward in this axial endoplasm to an anterior "fountain zone", 

 where they pass outward to join and extend the ectoplasmic sleeve. 

 Contraction at the anterior end, in the fountain zone, would 

 actively pull the axial endoplasm forward. Observations on naked 

 endoplasmic fragments confined in capillary tubes indicated that 

 multiple individual streaming units could exist side by side. 



The Allen group's hypothesis would seem to diminish the 

 fundamental distinctions between pseudopodial movement of the 

 lobose type and that of the filose type. Jahn and Rinaldi (1959) 

 have reexamined the latter phenomenon as exemplified in 

 Allogromia laticollaris . This genus is recognized by most 

 authors, including Jahn and Rinaldi, as a foraminifer but is placed 

 by Deflandre (1953, in the Grasse treatise) with the shelled amebae, 

 some of which exhibit the same sort of movement. From the 

 protoplasmic mass at the test opening of this organism a reticulum 

 of fine, branching and anastomosing pseudopodia extends out 

 over a radius of up to 15 mm. Because the pseudopodial 

 surfaces are studded with adhering particles of food and other 



