THE SEA SHORES 1 73 



like plants, are especially characteristic of the sea shores. 

 The so-called colonial animals along the coasts which, plant- 

 like in their growth though in no other way, live firmly fastened 

 and secure their food from the restless w'ater as it washes back 

 and forth, are the sponges, certain coelenterates, including the 

 hydroids, the corals, the sea-fans or gorgonians, the millepores, 

 the sea-pens or pennatulids, the umbellularians, the alcyona- 

 rians, the antipatharians, the colonial anemones, and some 

 other types, the polyzoans, the phoronids, the rhabdopleurids, 

 the cephalodiscids, and the colonial tunicates or sea-squirts. 



The sponges, all of which when alive possess a strong odor 

 disagreeable to us, though it may be attractive to the little 

 things on which they live, have the general mass (it can 

 scarcely be called a body) pierced by numberless small holes 

 leading into small tubes lined with extremely delicate hair-like 

 structures called cilia beating inward. These small tubes lead 

 into larger ones and these finally into an opening leading to 

 the exterior through which a constant stream of w-ater impelled 

 by the constant action of the cilia in the small tubes pours 

 outward. On its journey through the canals of the sponge 

 this water has lost a considerable portion of the nutritive 

 particles which originally it contained. One does not think of 

 muscular power in connection wdth the apparently motionless 

 sponges. Yet on the reefs at Bermuda at low tide I have fre- 

 quently seen the calm surface of the sea much agitated by a 

 stream of water coming from below which investigation showed 

 originated from the outlet of a large sponge. This food col- 

 lecting system of the sponges is very efficient, and other 

 animals take advantage of it. Jointed worms of many kinds, 

 one a much branched creature with a head on the end 

 of every branch, live within the canals, as do various small 

 crustaceans and brittle-stars. Barnacles, embedded in the 

 outer layers, and some crustaceans with similar boring habits, 

 as well as comatuhds attached to the surface, all take advantage 

 of the indraught of water into the small canals. 



The polyzoans, phoronids, rhabdopleurids and cephalodiscids 



