GROWTH AS INDIVIDUALS AND SWARMS 253 



Concentrations of eggs have also been given a modal value of one. In swarms, other than purely larval 

 swarms, where the modal value has been obtained directly from measurement, it is expressed by 2-mm. 

 groups up to 44 mm., and thereafter by 4-mm. groups up to 60 mm. 



The resuks of this treatment of the data are shown in Fig. 55 in which the open circles 

 represent the swarms in the East Wind drift and the solid circles the swarms outside it, the vast 

 majority of the latter from the Weddell or northern zone. Taking first the position in the north it will 



60 



56 



52 



48 



44 



42 



40 



38 



36 



34 



32 



30 



28 



26 



24 in 



22 3 



20 § 



IB 



16 < 



14 o 



12 2 



10 



8 



7 



6 



5 



4 



3 



2 

 I 



Fig. 55. Growth of the swarms expressed in terms of modal value, showing the persistent lag in developmental stature that 

 is found in the East Wind drift. Vertical scale from 10-44 rrini- inclusive in 2-mm. groups (e.g. 10 = 9-10 mm., and 

 44 = 43-44 mm.) and thereafter in 4-mm. groups (e.g. 48 = 45-48 mm.). For further explanation see text. 



be seen that spawning, in so far as it is represented by concentrations of eggs, Nauplii or Metanauplii, 

 begins in November, when the first eggs are found, and continues throughout December, January 

 and February until March. It is possible that it may last even longer, into April when the last sur- 

 viving young swarms consisting dominantly of Metanauplii are represented in our samples. From 

 January onwards, until June, they exhibit monthly a heterogeneous pattern of ages, the result 

 of the successive releases of batches of eggs over a period lasting at least 5 months. The majority 

 encountered from January to March, however, are represented principally by the First Calyp topis 

 stage. The first swarms in which the Fourth and Fifth Furcilias are dominant appear in March, 

 swarms dominated by the last larval stage, Furcilia 6, although present in June, not appearing on a 

 substantial scale until July. As a result of the slowing up of the growth-rate that accompanies the 

 winter phytoplankton minimum, the pronounced spread of the modal values encountered from 

 February to June undergoes a considerable degree of compression, which, becoming first apparent 

 in July, lasts virtually to the end of October. In November, however, when the phytoplankton blooms 

 there is a renewed spreading out of the modal pattern, the rapidity of the growth that takes place 

 from then until March being very striking, the modal values, concentrated about 16 in October, rising 

 to a maximum of 46 by the end of the second year's summer. The decline in phytoplankton values that 



