STUDIES UPON AMOEBA 
305 
tion between the excretory granules and this particular spot in 
the ectosarc. From this it is evident that the actual spot where 
the excretory pore forms from time to time when the vacuole 
contracts, is in an unchanging region in the ectosarc. To be 
sure this region flows from one position to another, but wherever 
it flows it retains its connection with the excretory granules and 
it continues from time to time to form a pore for the extrusion 
of the contents of the excretory vacuole. (See further discussion 
in Part II.) 
One is naturally interested to know the nature of these gran- 
ules which have such a close relation to the contractile vacuole, 
but my observations tell little of this. They resemble the ordi- 
nary cytomicrosomes in size and appearance ; I have found as yet 
no stain which difl"erentiates them from the cytomicrosomes; I 
have never seen any of these granules extruded with the liquid 
from the vacuole when it contracts. Yet the close association of 
this particular mass of granules with the excretory vacuole sug- 
gests that they have some functional relation to excretion. Com- 
parison with the conditions in Opalina makes this seem somewhat 
more probable. I have elsewhere described the condition in 
Opalina.*^ In the binucleated Opalinae there is an excretory vac- 
uole, often of irregular shape, lying chiefly in the posterior end 
of the body, and opening to the exterior at the posterior tip of the 
body by a pore which, even when closed, is often indicated by a 
sHght conical depression. There is almost always a posterior 
enlargement in the excretory vacuole, and around this vesicle are 
numerous granules closely resembling the cytomicrosomes, but 
staining a darker, less clear blue with Delafield's haematoxyhn, 
and with rubin S and also with borax carmine showing a darker 
red. Granules exactly resembling those around the vesicle, ex- 
cept that they are some of them barely perceptibly larger, lie 
in the lumen of the vesicle itself. They are clearly merely some 
of the surrounding granules which have dropped into tiie vesicle. 
The posterior vesicle of the excretory vacuole contracts infre- 
® Metcalf : The Excretory Organs of Opalina. Parts I and II, in Archiv f; 
Pro istenkunde, bd. x. 1907. 
