82 THE SHORE 



for the most part floating larvae, which can be carried 

 by ocean currents over wide stretches of sea, and 

 accordingly present relatively little variation of species 

 over each of our two great tropical oceans. Let the 

 naturalist collect a few groups only, but let him study 

 the growth of those few carefully on the spot in relation 

 to their environment. It does not matter whether he 

 knows the names of their groups, families, genera, 

 and species, or not. As we have already said, he 

 cannot go wrong, for such intensive studies of tropical 

 beasts have never been made. He will have the 

 satisfaction of knowing that he is at least adding some- 

 thing of high permanent value to biological science, 

 and he will be undertaking a study the interest in which 

 grows as the work continues. 



B. Coral Reefs and Islands. 



In the previous section we have already sufficiently 

 emphasized the paramount importance of ascertaining 

 the nature of the geological formation of any island 

 which may be visited. Islands divide themselves into 

 three classes, continental, volcanic, and coralligenous, 

 in accordance with the composition of their rocks, 

 though it is not always easy to separate them. A 

 continental island is one which, from the nature of its 

 rocks, or more generally from the considerable variety 

 of the animals and plants which live upon it, must 

 be supposed to have been at one time connected with 

 some continental mass of land, upon the surface of 

 which, according to our present views, a large variety 

 of animals and plants may be supposed to have been 

 evolved. Thus, for example, all the greater islands 

 of the East and West Indies must have been connected 

 at one time with their neighbouring continents. 



