1924] Ketssel: Amoebae of Culture Rats and Mice 499 



This forwaxd movement may be described as an ectoplasmic looping. 

 As represented in figure A, 1, the rounded amoeba shows at the most 

 only a narrow ectoplasmic margin. This rounded amoeba protrudes, 

 with almost explosive suddenness, a hyaline pseudopodium (fig. A, 2) 

 into which the endoplasm may later flow (fig. A, 3). In the progressive 

 movement, the pseudopodia appear blade-like in optical section, but 

 in reality are blunt lobes. They are inclined to be more pointed than 

 the pseudopodia formed when the amoeba is attached. In the forward 

 movement, the hyaline pseudopodium is fully formed before the vacuo- 

 lated and granular endopla.sm flows into it. At the posterior, or 

 attached end, a conical projection or attachment cone is often in evi- 

 dence (fig. A, 1). This appears to be used as a point of adhesion to 

 the substrate and as a point of leverage. As the endoplasm flows for- 

 ward, this root-like projection persists for a short time as a hyaline 

 structure (pi. 43, fig. 3). The amoeba then resumes a spherical or 

 ovoidal shape before it thrusts out another pseudopodium. The whole 

 process is then repeated. 



In progressive movement the pseudopodia are not all thrust out 

 in a constant forward direction, but lateral pseudopodia (figs. A, 8, 11) 

 or even posterior pseudopodia (fig. A, 14) may be formed. In the 

 observations made, however, a permanency of movement in a given 

 direction was maintained. The formation of these lateral and posterior 

 pseudopodia may indicate a reversing motor reaction such as is found 

 in ciliates, or it may indicate that the path, if observed for a sufficient 

 time, might represent a "flattened spiral" as described by Schaeffer 

 (1920). As in these amoebae there appears to be no constancy in the 

 formation of left or right-handed pseudopodia, it is not certain that 

 either a right or left-handed spiral would be retained. In progressive 

 movement, it is not common to see two pseudopodia (fig. A, 14) in 

 action at the same time, and this probably occurs only when the amoeba 

 changes its direction, as perhaps in a motor reaction. 



Pseudopodial formation during attachment. — In a cover-class 

 preparation, the amoeba often appear to be attached either to the slide 

 or to the cover-glass, as they may also adhere to a clump of bacteria 

 from which they are apparently making a continuous effort to become 

 free. Pseudopodia are then thrust out rapidly in aU directions, occa- 

 sionally as many as three or four being evident at one time (fig. B, 11 ; 

 pi. 43, figs. 1, 2). These pseudopodia are always hyaline and while 

 some present the pointed, blade-like appearance of the one formed 

 by amoebae in progressive movement (fig. B, 12), the broad, blunt, 



