CHAPTER X 
THE SIMPLER METAZOA 
128. Metazoa. — The Protozoa just studied are single, 
free, living cells, while the grasshopper is made up of thou¬ 
sands of cells. The grasshopper is called a metazoon (met-a- 
zo'on: Greek, meta,. later; zoon, animal) because there are 
many cells in its body. 
The Protozoa and the Meta¬ 
zoa are alike in that both 
take in food, breathe, give 
off waste matter, and repro¬ 
duce their kind. 
There are a number of 
organisms concerning which 
scientists disagree as to 
whether they are plants or 
animals. In zoology, these 
forms are known as Colonial 
Protozoa or simple Metazoa. 
We shall study two of these 
(gonium and volvox) and then examine the sponges, which 
all scientists agree are Metazoa. 
129. Gonium. — Gonium is an animal made up of sixteen 
separate cells held together by a mucilage-like secretion of the 
cells. Each cell works independently in getting food, breath¬ 
ing, giving off waste, and in reproduction. The colony 
moves by lashing the water with long protoplasmic threads 
(flagella), two of which project from each cell. The advan¬ 
tage in rate of movement resulting from the union of cells is 
152 
Figure 142 . — Gonium. 
