THE AMCEBA. 
191 
covered, and the evidence does not indicate its existence. It 
also appears indisputable that, when the Amoeba has extracted 
the nourishment from the food, it ejects what remains, but not 
at the spot where the food entered. This is done at the posterior 
extremity of the body (figs. 1, 2, 3, v ), where also the contrac- 
tile vesicles discharge themselves. Writers speak of an anal 
outlet at this point, but there i» no reason for believing in its 
presence. The particles appear to be simply forced out through 
the sarcode. 
When water is present in these vacuoles, the food appears 
to be surrounded by a clear space (fig. 16,/y). This, however, 
is not always the case. At other times the endosarc immedi- 
ately surrounding the vacuoles exhibits the same semiopaque 
aspect and numerous granules, as the rest of the endosarc. The 
nature of this clear area is open to the same doubt as that of 
the ectosarc itself, since Dr. Wallich and Mr. Carter are at issue 
on the point. Mr. Carter believes the ectosarc to be primarily 
and always a distinct tissue from the endosarc. Dr. Wallich 
on the other hand believes that the two tissues are mutually 
convertible. Thus the latter naturalist regards the transparent 
ectosarc, as endosarc which has been modified by prolonged 
contact with the surrounding watery medium, by a process 
analogous to coagulation. The result has been, as he supposes, 
that all the granules have been forced inwards into the more 
fluid endosarc. He accepts the same explanation of the 
diaphanous ring surrounding the food-particles, so far as that 
does not consist of mere water, regarding it as a consolidation 
of the endosarc through contact with the food and with the 
particle of water in which the food usually floats. Dr. Wallich 
explains in a similar way the disappearance of the food vacuole 
when the refuse food has been discharged from the hinder 
part of the body as above described. The food and water 
being no longer present to coagulate the endosarc surround- 
ing the vacuole, it gradually returns to the state of ordinary 
endosarc. These are questions involving careful and widely 
extended observations on the part of many observers, and 
even in the ablest hands, assisted by the most perfect instru- 
ments, the solution of them is attended with extreme difficulty. 
This much, however, may be considered certain, viz., that the 
food vacuoles are extemporized and not permanent cavities ; 
that their formation always commences at the surface of the 
animalcule ; that such formation may take place at almost 
any part of the body, save at what has been termed the villous 
or excretory region ; and that after they have discharged their 
effete contents at this region they finally disappear, never 
being reproduced at the same point, as is the case with the 
contractile vesicles. My own observations also confirm Dr. 
