436 DISCOVERY REPORTS 



of the larvae, everywhere, are developing in sub-zero temperatures, while the very early adolescents, 

 small whale food in the 1 6 — 20 mm. range, owing to the time of year in which they appear in the plank- 

 ton, spend virtually their whole existence in all four regions of euphausian abundance in water that 

 never rises above zero C (p. 75). 



7. Study of the vertical distribution of the larvae reveals that in oceanic water the eggs hatch at 

 great depths, possibly far below 2000 m. if the water is deep enough, the resultant larvae rising until 

 they reach the surface as the First Calyptopis stage. The subsequent development, Calyptopis One 

 to Furcilia Six, takes place in the Antarctic surface layer (p. 88 and p. 97). 



8. In the course of this ' developmental ascent ' as it has been called the new-born krill pass through 

 their Naupliar and Metanaupliar, and through the early part of their First Calyptopis, existence 



(P- 97)- 



9. In the northern or Weddell zone it is distinctly possible that the young krill are rising out of 



the northward and eastward-spreading Antarctic bottom water. If so, both this and the surface drift 

 must be involved in their horizontal dispersal to the east (p. 99). 



ID. Diurnal vertical movement in the larvae, once they reach the surface, is limited, taking place 

 for all practical purposes within the limits of the Antarctic surface layer. Such movement as there is 

 is perhaps most pronounced in the Calyptopis stages, but becomes increasingly less pronounced as 

 the larvae grow, the Furcilias, notably the later Furcilias, tending to be massed more or less per- 

 manently in the surface (50-0 m.) layer. With their limited diurnal movement the young stages, 

 especially the Furcilias, are readily inclined to be carried along in the surface drift (p. 105). 



11. As they climb towards the surface the larvae, as Second Nauplii, Metanauplii and First 

 Calyptopes, spend some considerable time, perhaps up to 30 days or more, in the warm deep current 

 which in most parts of the Antarctic has a southerly component, and which, therefore, plays an 

 important part in maintaining the population within the normal limits of its geographical range (p. 118). 



12. The absence, or virtual absence, of the krill from extensive areas of shelf water such as exist at 

 the head of the Ross Sea may partly be ascribed to the failure of the warm deep water to effect any 

 major penetration on to the shelf (p. 123). 



13. The astronomical abundance in which it exists and the key position it holds in the industry 

 and ecology of the Antarctic seas is revealed by a review of the vast and catholic multitude of its 

 predators (p. 126). 



14. The southern baleen whales feed principally on adolescent and adult krill over 20 mm. long 

 (the ' staple whale food '). In the early part of their sojourn on the feeding-grounds, however, notably 

 in spring, they augment their staple diet with large quantities of much smaller euphausians consisting 

 of mixtures of Sixth Furcilias and early adolescents (the 'small whale food') ranging from 11 to 

 20 mm. long. Whales have also been recorded feeding on the Sixth Furcilia in autumn (early April) 

 when this stage, in some abundance, first appears in the plankton of the western Weddell drift 

 (p. 138). 



15. It has been roughly calculated that between 1933 and 1939 the krill, at a conservative estimate, 

 were being grazed down by large baleen whales alone at the rate of about 38 million tons a year, a 

 figure which if expressed in terms of euphausians eaten comes to 47 million million (p. 145). 



16. The commencement of the phenomenal burst of growth that occurs in foetal baleen whales 

 during the last two months of pregnancy coincides with the arrival of their mothers at the richly 

 spread table of the Antarctic feeding-grounds (p. 147). 



17. The unevenness of its surface distribution, its patchiness or swarming habit, in so far as this 

 is a phenomenon displayed by the adolescents and adults and can therefore readily be observed 

 from the decks of vessels, is described in detail. In the northern zone, notably in the Weddell drift, 



