FRYER— FORMATION OF ALDABRA, ETC. 425 



suffering were conveyed to the Seychelles, where Drs Addison* and Power t made blood 

 preparations (films) which showed sporulating plasmodia, seeming to prove the nature of 

 the disease conclusively. 



A search was then made by the author personally for Anopheles, both by observing 

 the imagos and larvae, but this was absolutely without success and never during the entire 

 visit was an Anopheles found. 



There are therefore two alternatives : the first is that Anopheles arrived in April 1908, 

 propagated themselves so rapidly as to be able to infect over 100 people, and then died 

 out, also with such speed as to be extinct in September. It is conceivable that Anopheles 

 might not be able to persist at all in Aldabra, or that it might live for a short time and 

 then gradually die out, but that it should do so with such suddenness seems highly 

 improbable. This alternative therefore is not a likely one. 



The second is that Stegoinyia can be capable of a modified transmission of malaria. 

 It is almost certain that no sexual processes of the plasmodium can take place in 

 Stegomyia. It seems just possible however that this insect may act as a passive trans- 

 missor : it is present in such numbers even in the dry season that there is seldom 

 a moment, night or day, when the inhabitants of Aldabra are not being bitten, and 

 a transmission of blood is quite probable. Supposing this occurred when the plasmodia 

 were about to sporulate, or even just after, it seems possible that a fresh patient might be 

 affected. However, in the absence of sexual processes the stock of the protozoan would 

 probably become senescent, and ultimately die out. This is exactly what occurred, for at 

 the date of departure (end of January) there was not a single malarial patient in the atoll. 

 Supposing that this explanation could be proved correct it would explain the occasional 

 malarial epidemics which occur in other islands in which Anopheles is apparently 

 unknown. 



A few scattered notes have now been given concerning the fauna of Aldabra : as 

 however these could not be put in a very explicit form, it may be permitted to make 

 a short summary : — In the littoral fauna Aldabra resembles, or is perhaps somewhat 

 poorer, than any of the coral islands in the same region. The land fauna, probably on 

 account of the greater extent and age of the land, and also because of its more varied 

 vegetation, is larger than that of any of the neighbouring coral islands. It is composed 

 mainly of peculiar forms, but most of these are closely allied to Malagasy animals and are 

 such, with the exception of the land tortoise, as might easily have arrived by sea, and then 

 have altered somewhat under the fresh conditions found in an isolated land. 



* Chief Medical Officer. t Assistant Medical Officer and visiting Magistrate to the outlying islands. 



