14 



A NATURAL HISTORY OF THE SEAS 



by compression solid ground. When raised above sea 

 level, they form the well-known limestone cliffs. 



Whilst the vast majority of Protozoa must be thought 

 of as creatures of from one-hundredth to three-hundredth 

 of an inch in diameter, a few are just visible to the naked 

 eye. Large examples are the beautiful marine Noctiluca — 

 " night-light " creatures which when they congregate 

 in millions light up wide areas of the sea with a vivid phos- 

 phorescent glow. 



Foraminifera 



A sponge is fairly typified in the minds of most persons 

 by the common bathsponge which is so extensively farmed 

 in warm seas for toilet purposes. The form that is sold 

 in shops is but the horny skeleton of a large colony, each 

 individual being bound one to the other to form a single 

 solid mass. All are interdependent for the general 

 welfare on the other members of the community. 



To appreciate the true nature of a sponge one should 

 obtain a portion of one of the many species common round 

 our shores, or failing this, a branch of the vivid green 

 fresh-water sponge so common upon lock gates and canal 

 buttresses. A fresh specimen placed in water to which 



