STUDIES UPON AMOEBA 
309 
even bent around the nuclei so as partially to envelop them. In 
Hoplitophrv'a also the tub alar excretory vacuole lies along the 
side of the meganucleus. The intracellular tubules of some met- 
azoan cells similarly come into close relation to the nucleus.^ 
Do not these phenomena suggest that there is some functioaal 
value in such close association of nucleus and excretory vacuole? 
We have seen in Part T of these studies that the contractile 
vacuole and its surrounding granules in Amoeba proteus remain 
in constant juxtaposition with a particular spot in the ectosarc, 
and that it is in the pellicle over this spot that the minute tem- 
porary excretory pore appears in the repeated contractions of the 
vacuole. In the Amoeba we are now discussing t he vacuole rarety, 
if ever, contracts. This vacuole has a constant position in the 
very anterior end of the body. Bat this Amoeba movies in the 
manner described by Jennings and which is characteristic of A. 
limax, A. blattae, A. verrucosa, A. proteus and others, namel}^ 
by rolling forward, and not, as in most Entamoebae, by the ex- 
plosive or eruptive formation of pseudopodia.** In this roUing 
type of progression any given spot upon the ectosarc of the upper 
surface is constanth' moving forward till it reaches the anterior 
end of the body, when it moves downward to the lower surface, 
the animal continuing to roll forward over it until this same por- 
tion of ectosarc comes to be posterior and then again upon the 
upper surface. If the excretory vacuole were to retain a constant 
relation to a particular portion of the ectosarc it would have to 
rotate with the ectosarc, being first anterior, then ventral, then 
posterior, then dorsal, and so on. But the vacuole does not so 
rotate, remaining instead always at the extreme anterior end of the 
body. The vacuole, therefore, in this species, can have no con- 
^ I would not urge strongly this interpretation of the intracellular tubules of 
nerve cells and other metazoan cells as excretory. 
^ I have not studied the locomotion of this species of Amoeba with the closest 
scrutiny of each detail. I have not traced the course of any particular spot on the 
ectosarc to demonstrate that this Amoeba has the type of locomotion described 
by Jennings, but even without this demonstration the appearance is so exactly 
like that in A. limax and so entirely different from that of Entamoebae; that 
one cannot doubt the locomotion to be of the rolling type. The ectosarc rolls; the 
endosarc streams forward. 
