SECT. 4] 



BIOLOGICAL SPECIES, WATER- MASSES AND CURRENTS 



399 



sphere would have been provided. During warm epochs the belts of distribution 

 would have moved toward the poles, establishing isolated pockets of distribu- 

 tion in the northern oceans (there, forms would differentiate if they were to 

 remain isolated sufficiently long), while allowing circum-global exchange of 

 genetic material to take place south of the continents. 



SUBARCTIC ItBANSITOnJ CENTRAL I EQUATORIAL CENTRAL ^TRANSlTK>j 



SALINITY (%.) 



OK r&EN (ml/I ) 



^U/ 



/ 



TEMPERATURE CO 



SUBARCTIC SPECIES 40 



TRANSITION ZONE £ 200 

 SPECIES 



CENTRAL SPECIES 200 



50°N 40" 30° 20° 10° 0° 10° 20° 30° 40°S 



50° N 40° 30° 20° 10 



10° 20° 30° 40°^ 



Fig. 7. Abundance of certain euphausiids, belonging to four faunas, from a north-south 

 mid-Pacific track (Fig. 8) compared with salinity, oxygen and temperature profiles 

 from the same stations. 



