36 FRESH- WATER RHIZOPODS OF NORTH AMERICA. 



withdrawn and altogether disappear. The growing psendopods are cylin- 

 drical or digitate, with blunt extremities. They extend in all directions, 

 are usually more or less curved, and frequently branch. In this condition, 

 the Amoeba may present the appearance represented in fig. 2. 



Occasionally the rounded or ovoidal mass composing the body of the 

 Amoeba, after putting forth numerous processes in the manner above 

 described, withdraws the most of these, while a few others rapidly elongate, 

 and diverge on each side, and the animal may assume a shape reminding 

 one of a great spider. A specimen in this condition is represented in fig. 1, 

 pi. II. 



Commonly, while one or two, and occasionally more, of the pseudo- 

 pods, continue to extend and branch, others shorten and disappear, and the 

 principal mass of the body is diminished at the expense of the growth of 

 the advancing psendopods, and it may to a greater or less extent merge into 

 them. As the Amoeba advances through the extension of one or more prin- 

 cipal psendopods in a particular direction, the whole together becomes more 

 or less differentiated into an anterior and a posterior region. The posterior 

 extremity of the body, in its contraction through the flow of its endosarc 

 into the advancing psendopods, frequently assumes a more or less mammil- 

 lary appearance. In this condition, the Amoeba, in its form and branching, 

 may remind one of the antler of an elk, and such specimens are represented 

 in figs. 3, 4, pi. I. 



In the continued extension and branching of one or more of the chief 

 pseudopods, the Amoeba progresses more or less rapidly, the body appear- 

 ing incessantly to exhaust itself in the continued growth or elongation of 

 the pseudopods and in the production of new ones, while it is as incessantly 

 replenished by the contraction and melting-away of pre-existing pseudo- 

 pods. While the animal moves along, its direction may change at any 

 moment by the more active prolongation of any one of the pseudopods. 



The changes of form produced by the extension and branching of cer- 

 tain of the pseudopods, with the recession, melting-away, and total disap- 

 pearance of others, is endless. Sometimes the animal creeps onward in a 

 flowing manner with comparatively simple cylindroid form, occasionally 

 emitting a single pseudopod, on one side or the other. More commonly 

 in movement it assumes a dendroid or palmate form, or sometimes, diver- 

 ging from the directly onward course, it becomes more radiate in appearance. 



