162 CCELEN TER A TES. HYDRA-LIKE ANIMALS 
merits possible are such as take place in the expansion and 
contraction of the whole body. The tentacles wave about 
in the water and as the hydra 
expands, the body may move 
first in one direction, then in 
another. In this sense the 
hydra does not move about 
as does a grasshopper or a 
paramecium. At infrequent 
intervals, however, the hydra 
detaches itself and moves 
from place to place by at¬ 
taching the tentacles, then 
the base, then the tentacles 
much like a boy turning 
handsprings. 
141. Nutrition. — The hy¬ 
dra feeds almost entirely 
upon minute animals. The 
forms that furnish the greater 
amount of their food are shown in Figure 54. These 
animals belong to a much higher group of animals than the 
hydra; namely, the Crustacea, the group to which the cray¬ 
fish and crabs belong. 
These animals which have 
an exoskeleton like in¬ 
sects are rendered inac¬ 
tive by the stinging cells 
on the tentacles. The 
paralyzed animal is then 
brought to the mouth 
by the tentacles, Figure 
148, and swallowed. Within the body, the nutritive parts 
are digested by enzymes as in other animals and ab¬ 
sorbed, passing by osmosis to all the cells. The undigesti- 
of Hydra. 
