CHAPTEE XVI. 



THE DISTRIBUTION AND RELATIONS OF SHORE 

 ANIMALS. 



What does ''littoral" mean? Characters of the littoral fauna The 

 two other marine faunas Subdivisions of the littoral zone Dis- 

 tribution of British forms The geographical regions Origin of 

 littoral animals Evidence for and against a pelagic origin 

 Difficulties of a final decision Relations of littoral to terrestrial 

 and fresh-water forms Conclusion. 



WE have now completed our systematic survey of the 

 common animals of the shore, and as we began with a 

 preliminary study of the conditions of shore life, so it is 

 fitting that we should, in conclusion, return to the consider- 

 ation of some general points connected with the littoral 

 fauna. In the first place, we have not as yet strictly defined 

 the meaning of the word " shore," but have used it loosely as 

 meaning the area between tide-marks. It is, however, fairly 

 obvious that this area is not sharply marked off from the 

 area just beyond low-tide mark. Very little experience in 

 shore collecting shows that animals which in one area may 

 be found freely on the shore rocks, in another region can 

 only be found after storms, and thus obviously occupy 

 deeper water. We have noticed this with regard to Alcy- 

 onium and the beautiful plumose anemone (Actinoloba 

 dianthus), but it is true also of a great number of other 

 forms, and has in several cases given rise to active contro- 

 versies. Some particular authority gives water of a certain 

 depth for some animal, and this is quoted by others as a 

 final statement, and yet it is quite possible that in other 

 localities the same animal may occur in very different 



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