io 4 DISCOVERY REPORTS 



Spongiobranchaea anstralis. Found everywhere from the convergence to the coldest 

 regions. It is very evenly distributed, but is possibly a little commoner in the warmer 

 water than elsewhere. There are rarely more than one or two in a sample and there is 

 no evidence of any tendency to form shoals or local concentrations. 



Clione antarctica. This species also is widely distributed, but it is rather commoner 

 in cold than in warm water. It is occasionally found as far north as the convergence. 

 On the whole it is very evenly distributed, occurring generally in very small numbers 

 and showing no tendency towards forming local aggregations. 



Salpa fusiformis f . aspera. Found everywhere from the convergence to the Bellings- 

 hausen and Weddell Seas. Its distribution is not unlike that of Metridia, for it has been 

 caught in large numbers at all the night stations and at most of the day stations in the 

 vicinity of the South Orkney Islands. It seems that there is nearly everywhere a sprink- 

 ling of Salps, and here and there a dense patch. Catches in the South Sandwich region 

 have all been small, but big hauls have been taken off South Georgia and one large 

 aggregation has been met with in the Bellingshausen Sea. The shoaling tendency of 

 the Salps is of a different type from that of the "krill". The former seem occasionally 

 to be concentrated in large areas where the numbers reach a maximum in the centre. 

 A typical example is provided by seven successive stations (564-70), covering some 300 

 miles in the Bellingshausen Sea. At these the numbers of Salps taken were, respectively, 

 o, 4, 66, 550, 369, 57, o. Enphaiisia superba occurs in smaller, denser and more numerous 

 shoals. 



Chaetognatha. This group, which is principally made up of Eukrohnia hamata, is 

 found in the greatest numbers in the outer, warmer part of the Antarctic water, and the 

 largest catches have, in general, been those closest to the convergence. Large numbers 

 are not likely to be taken south of a line running from the South Shetlands to South 

 Georgia, but some quite large catches have been taken in the western Bellingshausen 

 Sea. The distribution of the Chaetognatha appears on the whole to be very regular, and 

 it would appear that Eukrohnia hamata, at any rate, does not tend to form shoals. This 

 species, according to Bigelow and Leslie (1930, p. 564), "ranges from Arctic to the 

 Antarctic in the Atlantic, being confined to the bathyplankton in low and mid- 

 latitudes". 



It will be seen from the foregoing notes that the macroplankton can be divided very 

 roughly into three groups : (i) those species which have a definite preference for, or 

 which are actually confined to, the cold water or high latitudes, (ii) those which are 

 definitely typical of the warmer water or lower latitudes, and (iii) those which may be 

 found everywhere and may be taken in maximum numbers in both the warmer and 

 colder regions. 



It has been explained that the Antarctic surface water in the greater part of these 

 regions is drifting mainly in an easterly or north-easterly direction, and, as we 

 should expect, the isotherms are roughly parallel to the direction taken by the oceanic 

 currents (see Fig. 22). In Fig. 21 lines are drawn to show the distributional boundaries 



