VERTICAL DISTRIBUTION OF LARVAE 329 



are such that they counterbalance any difference in the times spent in each, the population would tend 

 to be maintained in the same latitude. This does not imply, however, north and south movements in 

 the same longitude, for the animals will always be moving towards the east during the night under 

 the influence of the easterly component of the Antarctic surface water. The water movements to 

 the north of the Antarctic convergence are not so well known as those to the south and it is difficult 

 to say what effect vertical movements of animals might have on their horizontal distribution. 



VERTICAL DISTRIBUTION OF LARVAE 



The vertical distribution ot the larval stages of E. triacantha has not been examined in great detail, 

 since the material available is necessarily more limited than that for the adolescents and adults. This 

 is partly due to the restricted breeding period and partly to the narrow latitudinal range of the larvae. 



'2_ 



1.6 



20 



HOURS 

 00 



0.4 



0-1 

 SO- 



lOO- 



250- 



2 500- 



I N«, of 



H STAHONS 

 a. EXAMINED 



a O- 



SO- 



100- 



^ 



2SO- 



soo 



N «. of 



STATIONS 

 EXAMINED 



08 



L_ 



12 



CALYPTOPES 



^ 



T 



12 



I 



FURCILIAS 



NUMBER PER JSOm.HAUL 



23 



Fig. 12. The daily vertical distribution of calyptopes and furcilias from the N70V hauls. Only stations at which the larvae 

 occurred have been used in calculating the mean number per 250 m. haul. 



The data obtained from the material that has been examined are presented in Fig. 12. As in 

 Fig. 9 C the day has been divided in six 4-hourly periods and the mean catch per 250 m. haul calculated 

 for each depth range in these periods. In calculating these means only stations at which calyptopes 

 or furcilias occurred have been taken into account. 



This figure suggests that, although the calyptopis stages probably perform a diurnal migration, it 

 is confined mainly to the upper 100 m. The furcilias, however, show a more pronounced migration 

 that extends between 250 m. and the surface. No calyptopes have been taken from below 250 m. 

 and no furcilias from below 500 m. It has been mentioned above that some animals become sensitive 

 to light with increasing age (Gushing, 1951) and the fact that the calyptopes do not descend below 

 250 m. during the day may be due to the lack of sensitivity to light or it may be due to a lack of 



