THE OLDER STAGES 175 



regularly in the stomachs, Thalassiothrix antarctica fragments commonly, and Synedra as present 

 but rare. 



During a brief but very intense period of blooming of the diatom Stephanopyxis turris, in the 

 UUadulla region of New South Wales, Sheard (1953) noted that many specimens of Nyctiphanes 

 australis were taken with their ' food baskets ' filled principally with faecal pellets, apparently those 

 of C alarms finmarchicus, with which the flowering StephaJiopyxis was associated. He found too that, 

 in a small collection of euphausians brought back by the B.A.N. Z. Antarctic Research Expedition, 

 in the majority of the specimens of £^. superba, E. triacantha, E. spinifera, E.similis, Thysanoessa macrura 

 and T. vicina he examined, the chief constituents of the food baskets were again faecal pellets. These 

 findings led him to suggest that, although confirmation was required from larger sources of material, 

 a prime food source of euphausians in areas of high diatom production might well be the faecal 

 material of the grazing herbivores. If it were so, however, in so far at least as E. superba is concerned, 

 it is surprising that neither Barkley, with his wealth of Antarctic material, nor Hart, makes any mention 

 of it. 



Marshall (1954), referring to the intimate correlation between form and function in aquatic animals 

 and their ways of seeking, finding and collecting food, notes that E. superba with its fine thoracic 

 filter basket and strongly developed grinding mandibles is better equipped for deaUng with a phyto- 

 plankton diet than, for instance, is E. hanseni, an omnivorous species, existing probably on copepods 

 and a variety of other small animals, in which the thoracic filter is coarse and the molar parts of the 

 mandibles small. He notes too other striking anatomical diflFerences between the almost exclusively 

 herbivorous Antarctic krill and euphausians of the omnivorous or rapacious kind. 



The problem of the re-solution of silica in the sea is as yet little understood (Barnes, 1957). Cooper 

 (1952) points to the evidence that the skeletons of many though not all diatom species are resistant 

 to solution and for all practical purposes are insoluble while intact. However, he calls attention to 

 Hart (1934, 1942) on the feeding of E. superba, noting how thoroughly and rapidly this species seems 

 to be able to digest many of the more fragile and poorly silicified forms, adding that this provides 

 strong circumstantial evidence that re-solution of diatomaceous silica is a rapid process. He notes, too, 

 that freshly fractured surfaces of quartz and some mineral silicates are in a highly reactive state, 

 readily yielding 'soluble silica' on contact with water, and that in the sea much the commonest way of 

 exposing fresh silica surfaces by fracturing would occur in the guts of herbivores, such as E. superba, 

 which grind or triturate their food. 



It would appear distinctly possible, therefore, that the grazing of the multitudes of the krill con- 

 tributes something to the maintenance and recruitment of the enormous concentration of silicate 

 (Clowes, 1938) in Antarctic waters. 



The phytoplankton, on which the krill are so admirably equipped to feed, contains /^-carotene (Kon, 

 1958), and this (Fisher, 1958) they are able to convert to vitamin A and store, principally in their eyes. 

 It is from this preformed source that the whales, especially the blue whales (Braekkan, 1948), derive 

 the rich vitamin A content of their livers. 



Nemoto (1959) reports that in the summer of 1958 the vitamin A content of baleen whale liver 

 increased in the East Wind zone from west to east, being low between 60° and 100° E, gradually 

 rising between 100° E and 160° W, and reaching a maximum in the former sanctuary between 

 160° and 100° W. He suggests as 'a simple and bold explanation' that the vitamin A content of 

 Thysanoessa macrura, on which the whales (p. 48) are known to feed on the Pacific side, is higher 

 than that of E. superba. Other factors, however, could also be involved. The vitamin values, for 

 instance, might be expected to increase with the advance of the season as increasing nourishment is 

 taken by the whales. Many of Nemoto's high values between 160° and 100° W are in fact in 



