124 STUDIES IN INSECT LIFE, ETC. 



rise, and gradually rising till about the middle 

 of the afternoon. And again, there is a fort- 

 nightly rhythm, inasmuch as near the land the 

 sea is warmer in the summer just after the time 

 of new or full moon, and colder at the same 

 periods during the winter. 



Other rhythms might be pointed out, such as 

 those dependent on the intensity of sunlight, 

 and on the degree of salinity, which in turn de- 

 pends to a very large extent on the water circu- 

 lation of the sea. The pulsing-up of the Gulf 

 Stream is the direct result of this circulation and 

 affects not only the warmth but the salinity 

 of the waters on our western shores. ' The 

 water is saltest when the drift is strongest, in the 

 months of February to June, and is less salt 

 when the drift is weakest, in the months of No- 

 vember to February/' All these features have 

 a profound influence on the life of the ocean ; 

 and a remote influence on land animals whose 

 ancestry was marine. 



