42 THE STORY OF LIFE IN THE SEAS. 



Polyp with eight feathered tentacles gradually 

 unfolds itself, only to be slowly withdrawn into 

 the mass when the vessel is shaken or otherwise 

 disturbed. These Polyps form colonies, known 

 as Alcyonium digitatum. 



Now it is to be noticed that none of these 

 three examples of the sedentary Fauna can move 

 in the least degree from the rock or shell to 

 which they are fixed. When once the young 

 larva has taken up its position there it must 

 remain until old age or some disaster brings its 

 life to an end. When they are first hatched 

 from the egg that is thrust into the water by the 

 parent, they pass through a larval stage that, like 

 the Nauplius of the Barnacle, is active and free. 

 Then they are carried away from the parent 

 stock partly by their own active movements, but 

 more particularly by the tides and currents of 

 the sea- water. At last a change in their structure 

 occurs. They sink to the bottom, become at- 

 tached to a rock or stone, complete their meta- 

 morphosis, and remain anchored to the spot for 

 the rest of their lives. 



The number of different forms of animal life 

 which constitutes this sedentary Fauna of rocky 

 coasts is very great indeed. In addition to the 

 Barnacles, Worms and Alcyoniums, there are 

 numerous species of Sea-anemones, Sponges, 

 Corals, Zoophytes, Sea-squirts, and other forms, 

 and in all these cases the eggs give rise to free 

 swimming larvae, by which the distribution of the 

 species is effected. 



Another group of animals, which forms an 

 important feature of some rocky coasts, are the 



