CCELENTERATA. 



179 



The polyps cover up the shell occupied by the crab, thus con- 

 cealing it from its enemies and its prey. In return the polyps 

 doubtless profit by a share of the food broken to pieces by the 



FIG. 84. 



FIG. 84. Physalia, the Portuguese Man-of-war. After Agassiz. 



Questions on the figure. For what is this animal remarkable? To 

 what group of ccelenterates does it belong? Compare Huxley's figure of 

 the same animal (see Parker and Haswell's Zoology, Vol. I, p. 152, and 

 other reference texts). What various types of polyps are represented in 

 the colony? Compare with Fig. 85. 



crab, as well as by the change of place as the crab moves about 

 in search of food. Some anemones have living algae in their 

 entoderm cells which seem to help supply the animal with 

 oxygen in return for foods of other kinds. 



