128 AMEBOID MOVEMENT 



b 



Figure 44. Amo-eba flagellipodia, a, showing nucleus, 4 microns in 

 diameter, and four vacuoles. b, a pseudopod of three spiral turns which 

 in a few seconds grew into one of six spiral turns, c. d, a pseudopod of 

 a number of spiral turns, which a few seconds later took on a shape 

 shown at e. The tip of the pseudopod at / turned screw-like anti-clock- 

 wise, when looking at the tip and at the main body of the ameba. The 

 tip made one complete revolution in about three seconds. 



pseudopods formed become spiralized at one time or another of 

 their existence, the greater number of these being however rela- 

 tively immotile. Pseudopods frequently fall into spirals while 

 they are being extended. 



A better transition form between pseudopods and such flagella 

 as are found, for example, in the peranemas, could hardly be 

 imagined. The difference between, crawling and swimming would 

 seem to be merely a matter of speed of movement of the pseudo- 

 pod. 6 But important as such a transition form is for theoretical 



6 The gap between the rate of movement of a pseudopod and that of a 

 flagellum is however very wide. Insofar as the character of the move- 

 ment is concerned, pseudopods such as those of flagellipodia, probably re- 

 semble the flagella of the soil ameba and of flagellates. But the very 

 much greater speed of contraction of a flagellum and the presence of a 

 special organ (blepharoplast) at the base of the flagellum, and their con- 

 nection with the nucleus, indicates that a special mechanism is necessary 

 to cause the rapid contraction. A flagellum appears to be a pseudopod 

 supplied with something like nerve tissue and a ganglion capable of setting 

 free a rapid succession of impulses. 



