MICROSCOPIC ORGANISMS IN INTESTINAL CANAL, 263 
contractile vesicle is at once distinctly visible within them; in 
others such a structure can only be detected with extreme 
difficulty, and in still others it appears to be absent. The same 
inconstancy seems to prevail in regard to the presence of a 
nucleus and nucleolus. Generally, I believe, a clear nuclear 
area is visible at a comparatively early stage, but a differentiated 
nucleolus often does not appear until much later; when it does 
appear it is as a flattened circular disc in the nuclear area. The 
rate of growth in the Amcebe and the size ultimately attained 
ere the occurrence of sporangic formation varies very much, 
apparently in accordance with the nature of the medium. In 
favorable cases it is wonderfully rapid, and where the growth is 
considerable, it is usually associated with further development 
of the nucleus (Pl. XVIII, fig. 10). A division of the nucleolus 
occurs, and the resultant bodies move somewhat apart, so that a 
pair of greenish discs replace the originally solitary one. 
Farther than this the nuclear area seems to become differen- 
tiated from the rest of the body-substance by a boundary layer, 
and a cross partition of similar nature passes inwards to separate 
the nucleoli (Pl. XVIII, fig. 15). 
Fic. 11.—Cornuate Amcebe x 180. 
The characters of the movement also vary greatly in different 
specimens, and in one and the same specimen at different times. 
Sometimes it is of a free flowing character, the organism moving 
rapidly forward by means of successive protrusions of its sub- 
stance. In other cases we find such movement alternating with 
a more sluggish action, in which the body presents an irregularly 
lobed or cornuate form, and only gives origin to limited exten- 
sions (Fig. 11). This condition frequently seems to coincide 
with defective nutrition, as the addition of fresh nutritive matter 
will often cause it to be exchanged for free progression. In 
still other cases again the body assumes a peculiar flattened 
scale-like condition, adhering by one surface to the glass of the 
slide, and moving forward with a slow gliding motion, accom- 
panied with comparatively little change of form (Fig. 12). In 
such cases the free surface often shows curious linear markings 
due to the presence of longitudinal thickened ridges. Three dis- 
