ZOOPLANKTON OF DIFFERENT REGIONS 



231 



plankton content of the remaining groups has a remarkable sameness, although we may 

 note that Euphausia superba, E.frigida, Limacina helicina and Salpa fusiformis are more 

 abundant in the Weddell Sea water groups than in that of the Bellingshausen Sea water, 

 or the water of its mixture in Group II. The distribution of the zooplankton organisms 

 in relation to the phytoplankton will be further discussed in Part V. 



Table XXXIX 



Showing the overage number of the principal zooplankton species taken at stations in the 

 different phytoplankton groups. Outstanding features shozvn in heavy type. 



* Numbers given for the top 250 m. only expressed as an average per 50 m. haul. 



VERTICAL MIGRATION 



The diurnal vertical migrations of plankton animals have been known and studied 

 in the northern hemisphere for many years. Russell, who has made such detailed studies 

 of these movements in the Plymouth area, published (in igzya) a general survey of the 

 subject up to that time giving a very full bibliography. Since then a number of other 

 papers have appeared, amongst which may be mentioned those by Russell (1927-34), 

 and by Gardiner (1933 and 1934), Nicholls (1933) and Clarke (1933). 



30-2 



