AMEBOID MOVEMENT 31 



great ease at its posterior end. But what the conditions are 

 which are necessary for the formation of a uroid, a structure 

 which it may be added, exists in many species of amebas (and 

 perhaps also in Cercomonas), is quite unknown. 



In contrast to the amebas thus far discussed from the point of 

 view of the transformation of endoplasm into ectoplasm, there are 

 a number of species in which two distinct methods of endoplasmic 

 transformation occur typically. Among these species are the 

 small Amoeba radiosa (Figure 7), A. bigemma (Figure 8) and a 

 new species which for convenience will be referred to as bilzi. 



It is well known that radiosa has two stages : a more or less 

 clavate shaped stage in which the ameba creeps along the surface 

 of some object (Figure 7, d) ; and a stage in which a number 



Figure 8. Amoeba bigemma, after Schaeffer. a, usual form in locomo- 

 tion, showing the numerous pseudopods, vacuoles, nucleus and food body. 

 b, rayed stage frequently assumed when suspended in the water. The 

 pseudopods in this stage are clear, slender, and more rigid than those in 

 stage a. c, an excretion sphere attached to a twin-crystal characteristic 

 of this ameba. d, the nucleus, consisting of a clear nuclear membrane 

 and a mass of chromatin granules in the center, e, a small sphere at- 

 tached to a crystal. /, a twin crystal unattached to a sphere. Length of 

 a, 150 microns; of d, 12 microns; of /, 2 microns. 



