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 apertures 

 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 

 obtain their food from microscopic creatures 

 and nutritive particles in the water, and in order 

 to get enough they have to pass large quanti- 

 ties 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 

 jostling particles of living matter inside the cells 

 to the people themselves, we would compare a 



