OF SOME COMMON MARINE ANIMALS. 



249 



in different seas under different conditions. The work will have to be done 

 in each great area, such as the North Sea, the English Channel, and the 

 Irish Sea, independently. This is a necessary investigation, both biological 

 and physical, which lies before the oceanographers of the future, upon the 

 results of which a rational conservation and exploitation of our national sea- 

 fisheries may depend. 



My own contributions to the subject so far deal only with the shore and 

 shallow-water animals of the littoral and the top of the Laminarian zone, 

 and I shall give here merely a few examples from different groups of animals 

 and plants, and from different localities, mainly to demonstrate the enormous 

 abundance of some of the commonest, and therefore the most important, of 

 the animals and plants on what are sometimes called our " barren " sea- 

 shores. I shall first take the cases of a worm, a crustacean, a mollusc, and 

 an ascidian — all forms that are free-swimming when young but fixed in the 

 adult condition, and all of value as food of marketable fishes. 



Sabellakia. 



The gregarious Polychret Annelid Sabellaria alveolata is present in great 

 abundance on many parts of the coast of ]Sorth-West Europe, generally on 



Fig. 1. — Subelluriu alveulata, from Ililbre Id., n.ii.size. 



shores where stones or patches of rock crop out in proximity to sand and where 

 strong tidal currents disturb the sand and carry the suspended grains along 

 in quantity. The worms stick the sand-grains together to form the tubes in 

 which they live and which adhere to one another so as to build up solid 

 masses of a porous, crisp and brittle material, which crumbles to a certain 

 extent when walked upon, but which is constantly being renewed and has 

 its injuries repaired by the living worms within, and must, therefore, have 

 a very considerable effect in some places in protecting the rocks or shore 



