308 
MAYNARD M. METCALF 
II. A NEW SPECIES OF AMOEBA, PARASITIC IN TADPOLES 
For the sake of comparing the excretory vacuole of this new 
Amoeba with that described in chapter I for Amoeba proteus, 
I include here an incomplete description of this form. I cannot 
give a complete description because by mistake my notes, draw- 
ings and measurements of these animals were left at my summer 
laboratory on the coast of Maine, and cannot now be obtained. 
This minute Amoeba, parasitic in the recta of tadpoles of Bufo 
cinereus, Rana esculenta and Bombinator pachypus — all from 
Wiirzburg, Bavaria — is spatula-shaped with the posterior end 
mammillated much as in large Amoeba proteus (fig. 24). At its 
extreme anterior end, the broader end, is a large vacuole com- 
pletely filling this part of the body. Close pressed against the 
posterior face of this vacuole lies the nucleus. The nucleus and 
vacuole are both slightly flattened on their contiguous surfaces, 
doubtless by pressure. The nucleus is not of the ordinary pro- 
teas type, but is of the type characteristic of the Entamoebae and 
most other minute Amoebae. Just inside its nuclear membrane 
are numerous chromatin granules. It has a well defined caryosome, 
with chromatin granules just inside the caryosome membrane. 
A caryole is present. A few irregularly scattered chromatin 
granules are found in both caryosome and nucleus proper, not 
abutting on the membrane. 
One point of interest in this connection is that I have never 
seen the anterior vacuole contract, though I have studied several 
dozen individuals at different times and for considerable periods 
at a time. The vacuole rarely, if ever, contracts when studied 
on the slide, either in undiluted fluid from the rectum, or in nor- 
mal salt solution containing all the rectal contents. Even if it 
seldom contracts, such a vacuole must be of assistance in excre- 
tion, since its contents are separated from the circumambient 
wacer by merely the thinnest film of protoplasm. 
The constant relation in position between nucleus and vacuole 
in this species is also of interest. I have shown for the binu- 
cleated Opahnae that when the excretory tubule (vacuole) is well 
developed, its anterior portion lies touching the nuclei, and is 
