NORTH ATLANTIC PLANKTON. 41 



more into the easterly drift of water that continues the 

 influence of the Gulf Stream up to the Irish coast. On 

 successive days the average temperature was 37°, 49°, 

 49°, 52°, 54°, and 55° F. 



The influence of the change of temperature upon the 

 organisms was most marked, especially in the case of the 

 cold Labrador current, outside the Straits of Belle Isle. 

 In this case, if we had had no thermometer, and had not 

 been able from fog or other reasons to ascertain our 

 position, I believe it would have been possible to recog- 

 nise that we had entered the Labrador current by the 

 microscopic contents of the tow-nets. 



It is a question how far the Gulf Stream can be said to 

 influence the surface fauna in the latitudes where we 

 crossed the N. Atlantic. Although no longer a clearly 

 marked warm current east of long. 40° W., still it merges 

 into, or is continued onwards as, a surface drift of warmer 

 water (due to the prevalent winds) eastwards and north- 

 wards to the British Islands and to the coast of Norway, 

 reinforced perhaps by Bennell's current coming up from 

 the Bay of Biscay. In this way the Atlantic drift current, 

 whether called Gulf Stream or not, must have considerable 

 influence upon the nature of the plankton in the north- 

 eastern part of the Atlantic, and we know that pelagic 

 organisms more commonly found in regions further south 

 and west are not infrequently carried to the west coasts 

 of Ireland and Scotland. 



The surface fauna of the Gulf Stream has been explored 

 by Mr. Alexander Agassiz and other American naturalists, 

 while the northern part and the southern sub-tropical part 

 of the North Atlantic have been more or less thoroughly 

 investigated by the Prince of Monaco, the naturalists 

 of the German Plankton Expedition, and others; but there 

 is a large central area between w T est longitudes 20° and 45° 



