THE SCHOOL OF THE SHORE 37 
shore animals. So these have to be on the 
qui vive, they must feed while they can, and 
take as much as they can. No doubt they can 
get a good living, but they cannot get it easily. 
One of the most important lessons that the 
inhabitants of the shore have to learn is to be 
always on the alert, and to make the most of 
their chances. 
Let us take some particular cases of food- 
getting. Encrusting the rocks in many places 
there is the Crumb-of-Bread Sponge (Hali- 
chondria panicea) with large exhalant aper- 
tures where the water is swept out, and minute 
pin-prick holes all over the surface by which 
the water is swept in. After their early youth is 
past, sponges are fixed animals, and one natu- 
rally thinks of them as easy-going. But they 
have to work hard for their living. They ob- 
tain their food from microscopic creatures and 
nutritive particles in the water, and in order to 
get enough they have to pass large quantities 
of water through their body every day. If an 
animal’s body be compared to a city, and the 
tissues to streets, and the cells composing the 
tissues to houses and workshops, and the jos- 
tling particles of living matter inside the cells 
to the people themselves, we would compare a 
