4 o 4 DISCOVERY REPORTS 



Euphausia triacantha, E. vallentini and E. frigida (Tables XVIII, XIX and XX) 

 occurred only in very small numbers for they are too large and active to be caught to any 

 large extent in the 70-cm. nets. However the figures show that E. triacantha was taken 

 near the surface as well as at other depths in March and September, and at moderate 

 depths in other months. E. vallentini was taken near the surface only in March and E. 

 frigida in each month except December, when no specimens were taken. The data from 

 8o° W suggest that these three species are not confined to the warm deep water in 

 winter, but there is not sufficient material to make this certain. However, as the species 

 of Euphausia are important constituents of the plankton I have examined some records 

 from other sources. Mr D. D. John has kindly shown me his analyses of the catches of 

 Euphausia taken during the second commission of the ' Discovery II ' (1931-33) and lt is 

 evident from these that all three species are to be found near the surface at any time of 

 year. E. triacantha has been taken in the upper layers in various localities in February, 

 April, May, June, September, November and December; E. vallentini in February, 

 April, May, June, September, October and November; and E. frigida in January, 

 February, April, May, June, September, November and December. This of course does 

 not prove that they live at exactly the same average depth at all times of year, but it does 

 seem certain that there is no wholesale retirement into deeper water such as we see for 

 instance in Calanus acutus. 



The remainder of the species which were identified and counted (Clione, Auricularia, 

 etc.) were so scarce that they must be disregarded here. 



EXAMPLES FROM OTHER PARTS OF THE ANTARCTIC 



The annual vertical migration exhibited by Rhincalanus gigas, Eukrohnia hamata, and 

 Calanus acutus is of considerable importance. In the preceding pages it has been shown 

 only that this migration took place in 8o° W in 1934. It would be extremely surprising 

 if a species undertook a mass movement on this scale in one locality in a particular year 

 and did not act in the same way throughout the Antarctic every year. That is to say such 

 an extensive migration is not likely to have been merely the result of any unusual hydro- 

 logical conditions in that year or any peculiarity associated with that locality. However, 

 if a few other samples, taken in other years and in other parts of the Antarctic, show the 

 same difference between the summer and winter distribution, there can hardly be any 

 further doubt that the annual migration is everywhere a normal characteristic of these 

 species. 



Apart from the work in September 1934 there have not been many occasions on 

 which the Discovery Committee's ships have collected plankton samples in winter, but 

 in September 1928 the 'William Scoresby' worked a number of stations around South 

 Georgia and between South Georgia and the Falkland Is., and in the winter of 1932 the 

 ' Discovery II ' gathered much material in the course of a long circumpolar voyage. 



It appeared to me sufficient for the present purpose to contrast the samples from a 

 pair of winter and a pair of summer stations taken by the ' William Scoresby ' near South 

 Georgia, and to make similar comparisons between some summer and winter samples 



