436 



CEYLON PEARL OYSTER REPORT. 



these, and are therefore presumably done on very much the same lines, so as to be 

 fairly comparable with ours ; and, secondly, because the Maldives are a group of 

 Coral-formed oceanic islands in contrast to Ceylon, which is continental and geologi- 

 cally a part of India. The comparison between a shallow-water (under 100 fathoms), 

 continental-coast fauna and that of a group of oceanic coral islands, only, on the 

 average, some 400 miles apart, in the same latitudes and the same sea, but separated 

 by deep water, ought to be instructive. 



The following table shows the number of species in the chief groups which are 

 recorded in both series of Reports : 



There are evidently marked differences here, and some of them at least seem 

 susceptible of explanation. A group of oceanic coral islands must clearly have been 

 populated from some of the surrounding older continental coasts,* and the nearest of 

 these to the Maldives are Ceylon and the southern end of India, some three to five 

 hundred miles distant, t There are two dominant factors that will play an important 

 part in determining which animals from the neighbouring continent will form part of 

 the new population, viz. : (1) The means of transport possessed by the animals 

 either in the adult or the larval condition, and (2) whether or not the conditions 

 existing on the island are sufficiently favourable to the migrating animal on its arrival 

 either as an adult or a larva. 



Looking at the table we find that the total number of animals is much greater in 

 the recorded Ceylon fauna than in that of the Maldives, but that in certain groups 

 the Medusae, Actinozoa, Gephyrea, Cirripedia, and Macrura the Maldivian 

 numbers are the greater; while in other groups such as Hydroida, Alcyonaria, 

 Echinodermata, Platyelmia, Copepoda, Amphipoda. Isopoda, and Mollusca the 

 Ceylon list markedly predominates. 



Oceanic or pelagic groups, as would be expected, and coastal animals of active 



* We may assume that even if Mr. GARDINER'S view is correct, that the Maldives are based upon an 

 old continental platform cut down by currents to a depth of some 2000 fathoms, none of the original 

 continental animals have lived on to appear amongst the inhabitants of the coral reefs. 



t Of course, some species may have come from the much more distant African coast. 



