CHAPTER II 
THE LIFE OF THE SLIGHTLY COMPLEX ANIMALS 
13. Colonial Protozoa.— When one of the simplest animals 
multiplies by fission, the halves of the one-celled body sepa- 
rate wholly from each other, move apart, and pursue their 
lives independently. The original parent cell divides to 
form two cells, which exist thereafter wholly apart from 
each other. There are, however, certain simple animals 
which are classed with the Protozoa, which show an inter- 
esting and important difference from the great majority of 
the simplest animals. These are the so-called colony-form- 
ing or colonial Protozoa. 
These colonial Protozoa belong to a group of organisms 
called the * Volvocine. The simplest of the Volvocine are 
single cells, which live wholly independently and are in 
structure and habit essentially like the other Protozoa we 
have studied. They have, however, imbedded in the one- 
celled body a bit of chlorophyll, the green substance which 
gives the color to green plants and is so important in their 
physiology. In this respect they differ from the other 
Protozoa. Among the other Volvocine, however, a few or 
many cells live together, forming a small colony—that is, 
* These colonial organisms, the Volvocinw, are the objects of some 
contention between botanists and zodlogists. The botanists call them 
plants because they possess a cellulose membrane and green chroma- 
tophores, and exhibit the metabolism characteristic of most plants ; but 
most zovlogists consider them to be animals belonging to the order 
Flagellata of the Protozoa. In the latest authoritative text-book of 
zodlogy, that of Parker and Ilaswell (1897), they are so classed. 
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