Mr Fryer, Aldahra and neighbouring Islands. 348 



do not increase indefinitely in size though the land continues 

 to be cut down as far as low water mark. This point will be 

 further illustrated by the atoll of Cosmoledo, which will be 

 described later. The structure of Aldabra has now been described, 

 and before proceeding further it may be mentioned that any 

 land connection with Madagascar is shown to be obviously 

 impossible. 



The Flora and Fauna of Aldabra must be treated very briefly 

 for the collections are not completely worked out. 



Flora. 



The Flora contains, oecologically, the following sections : 

 (1) Pemphis jungle which grows on metamorphosed rock and 

 contains little but Pemphis acidula. (2) Open country jungle 

 which contains a varied vegetation of Madagascar origin. (3) Man- 

 grove swamp containing three genera of Rhizophoraceae and 

 also the pseudo-mangroves Avicennia, Sonneratia and Carappa. 

 (4) Shore zone containing typical coral-sand plants such as 

 Tournefortia argentea and Scaevola koenigii. The zone owes 

 its origin to the fact that sand is blown on to the land from the 

 reef and forms a little soil near the shore. 



Fauna. 



The Mammalia, as regards indigenous species, are represented 

 by two bats only, though one Pteropus aldabranus is peculiar. 

 Reptiles comprise the Giant Land Tortoise (Testudo daudinii), 

 the Green Turtle (Chelone mydas), the Hawksbill (Chelone 

 imbricata), two species of Gecko and a Skink. The distribution 

 of the Giant Land Tortoises affords an interesting problem. They 

 have been found in recent times on the Seychelles, the Mascarenes, 

 Madagascar, Aldabra, Assumption and Cosmoledo. Their presence 

 on continental islands such as the Seychelles is easily accounted 

 for by the previous land connection, but this explanation will 

 not apply to islands of purely oceanic origin such as Aldabra. 

 The fossil bones on the latter atoll appear to prove that they 

 do not owe their distribution to transport by man : they are at 

 present too large to drift on wreckage or logs, or if drifted before 

 their large size was evolved, then they present a wonderful case 

 of parallel evolution. The matter still awaits a satisfactory 

 solution. 



Amphibia are absent from Aldabra and the fish though speci- 

 fically numerous call for no special mention. 



The land invertebrata are at present being worked out but 

 it may be mentioned that the majority seem to be derived from 

 Madagascar: indeed it may be said that the whole land fauna 

 with the exception of the Giant Land Tortoise is such that it may 

 have been obtained from neighbouring lands without necessitating 

 any former continental connection. 



