Knowledge of the Amodhx. 115 



The latter Is widened, during the flow of the Amoeha, at the 

 posterior end, by all sorts of processes, lobes, hairs, &c., which 

 often give the Amoeba a peculiar aspect, and have led to the 

 establishment of distinct species*. The sarcode here becomes 

 so tough that as the Amceba hastens forward it draws into 

 threads, if the expression may be allowed. 



If the direction of movement is reversed, the previous poste- 

 rior extremity begins to flow, and the most tenacious proto- 

 plasm occurs on the opposite side. These conditions may be 

 equally well studied on the lobate pseudopodia, as also during 

 the retraction of the pseudopodiura, on the surface of which 

 all sorts of humps and folds are produced. 



A tougher cortical zone of this kind is actually to be seen 

 in the forms here under consideration. When there is a 

 centripetal pressure acting uniformly, it surrounds the whole 

 Ama'ba like a membrane ; if the pressure ceases on all sides 

 the Amoeba flattens into a disk, the cortical zone liquefies and 

 flows together into a clear border of more fluid sarcode ; but 

 if the pressure acts on one side, the liquefaction takes place 

 only on the opposite side, and the mode of movement which 

 may be called the flow of the Amoeba is produced. 



In the formation of individual pseudoj)odia (see A. tentacu- 

 lata) it is only a few spots that are subjected to these condi- 

 tions, and in accordance with this the tougher cortex dissolves 

 only at certain points, making way for the issuing softer 

 sarcode. 



EXPLANATION OF PLATE IS. 



Figs. 1-8 relate to Amaha tcntaculata. 



Fiy. 1. An A. tentaculata with many pseudopodia. 



Fig. 2. Another, 0'12 uiiliiin. long, under a higher power (Hartnack 

 eyepiece o, objective lU immersion) and drawn with the 

 cuDwra lucida. It shows the cortical zone (r «), the pseudo- 

 podia (i)s) on their cones, and at h a cone of which the 

 pseudopodium has been retracted (crater). 



Fig. o. A portion of an Aniaha with three pseudopodia, highly mag- 

 nihed. 



Fig. 4. A specimen on which a number of craters (k) are to be seen. 



Fig. o. A specimen in which the cortical zone is dissolved. 



Fig. 6. A flowing Amceha tciitaculata, in which the nucleus (?*) is very 

 distinctly visible. 



Fig. 7. Another, in which three pseudopodia (;>.s) are still retained on 

 the advancing part. 



Fig. 8 A. A pseudopodium with its cone, m, the soft interior mass ; b, 

 the cortex ; p, the pseudopodium. 



Fig. 8 b. A pseudopodium in course of being retracted. 



Figs. 9-17 relate to Amaba aciinophora. 



• These structures have recently been referred to by i^ngelmann 

 (Onderz. Physiol. Lab. Utrecht, Deel vi. Afl. 2, St. 4). 



