UNICELLULAR ANIMALS. 91 
possibly the clear fluid with which they are filled may be a spe- 
cial secretion with solvent action on food. 
Fia. 38, 
Fias. 34 to 40.—In the following figures d, denotes disc ; 
pp, peristome ; vc, contractile vacuole; wf, food- 
vacuole ; vs, vestibule ; cf, contractile fiber; c, 
cyst ; nc, nucleus ; cl, cilium. 
Fig. 84.—A group of vorticelle showing the creature in 
various positions (A, 3). 
Fia. 35.—The same, in the extended and in the retracted 
state. (Surface views.) - 
Fic. 36.—Shows food-vacuoles ; one in the act of inges- 
. ‘ion. 
Fic. 37.—A vorticella, in which the process of multiplica- 
tion by fission is begun. 
Fie. 38.—The results of fission ; the production of two in- 
dividuals of unequal size. ; 
Fia. 39.—Ilustration of reproduction by conjugation. 
Fie. 40.—An encysted vorticella. 
Situated somewhat centrally is a horseshoe-shaped body, 
with well-defined edges, which stains more readily than the rest 
of the cell, indicating a different chemical composition; and, 
from the prominent part it takes in the reproductive and other 
functions of the creature, it may be considered the nucleus 
(endoplast). 
Multiplication of the species is either by gemmation or by 
fission. In the first case the nucleus divides and the fragments 
are transformed into locomotive germs; in the latter the entire 
animal, including the nucleus, divides longitudinally, each half 
becoming a similar complete, independent organism. Still an- 
