iv Transactions of the South African Philosophical Society. 



Atlantic, as this branch, as it proceeds northwards, becomes mingled 

 with the return current of the South Atlantic equatorial to form the 

 Benguela Stream which is ultimately carried over, perhaps partly as 

 a cold undercurrent, to the coast of South America, part passing 

 through the Carribean Sea into the North Atlantic. 



If then marine pelagic fauna is determined by its environment 

 like other faunas, and if, like other environments, there are great 

 factors within this determining the geographical distribution of the 

 contained forms of life, it will be readily understood that the key to 

 the character of the marine fauna of the Cape is to be ultimately 

 found in the peculiar features of its sea, which have just been 

 enumerated. Before, however, passing on to this, it will be neces- 

 sary to consider these features in more detail. 



Some years ago, in view mainly of the great importance of a 

 knowledge of the currents and changing character of the sea for 

 a determination of the laws which regulate the occurrence migration 

 and habits of fish and other forms of sea-life, a series of temperature 

 observations were begun at about twelve different stations round the 

 coast ; and it has been observed that the waters of the east coast 

 differ very considerably in temperature from those of the west coast, 

 and further, that while there is a gradual cooling of the Agulhas 

 current as it proceeds southwards and westwards, there is a very 

 abrupt change between the stations in False Bay and Table Bay, 

 showing that this is the meeting-place of two great bodies of .water 

 of different origin. 



The details of this transition can be shown by the result of a 

 series of observations of sea temperatures taken for a number of 

 years at the Eoman Rock Lighthouse in False Bay, and at Eobben 

 Island in Table Bay. The following diagram is drawn up from the 

 data and shows the mean monthly temperature of the respective 

 places for a period of three years. It will be observed that in 

 summer there is a difference of about 6°, while in winter there 

 is a close approximation of the curves of temperature. 



Another diagram will show the details of the variation of tem- 

 perature at points between these two stations at practically the same 

 time. It is drawn up from observations taken every ten minutes on 

 board the Pieter Faure when on passage from Table Bay to False 

 Bay. In conjunction with the temperature curve is shown one 

 indicating the variation in salinity of the sea-water. 



Another diagram drawn up from a series of observations made by 

 the mail steamer between Cape Town and Cape Hanklip illustrates 

 the same phenomenon. 



I draw your particular attention to this' variation in temperature 



