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DEPARTMENT OF THE NAVAL SERVICfJ 



with the shallow- coastal water; and (4) that another portion passes up the gully- 

 leading to the St. Lawrence gulf but keeping mainly to the north side of the gully. 



Its centre of abundance (fig. 3, closely placed lines) is then the deeper part of 

 the northern oceanic (boreal) water which flows to the south around the Newfound- 

 land banlvs. It is carried by the latter into the coastal water and beneath the Gulf 

 Stream. In the coastal water it must speedily perish, but in the Gulf Stream, the 

 smaller individuals at least find suitable conditions. The Gulf Stream on its way to 

 the north would seem to receive fresh additions of this species from the boreal water 

 beneath. The numbers obtained in the open vertical hauls from the south to the north 



Fig. 3. 



-Distribution of S. maxima, July-August 1915. Zones show frequencies of 1 to 5, 6 to 10 and 10 



and over per station. 



are 4, 5, 5, 7 at stations 44, 56, 74 and 75, respectively, showing an increase in the 

 number at the north. This may explain how the fauna of the Gulf Stream, as it 

 passes to the north, changes from tropical to boreal, the change in temperature killing 

 the tropical forms which are replaced by the boreal forms that enter the stream as 

 young individuals from the boreal water below. The growth of the boreal forms pro- 

 ceeds pari passu with the change in temperature, and they find themselves constantly 

 in water of suitable temperature for their continued existence. 



