THE DISPOSITION OF THE FILM 253 



Humpbacks formerly provided the greater part of the season's catch at South Georgia, 

 but of late years their capture has only been permitted by special licence when other 

 species are scarce. Few, therefore, have been examined for the presence of skin film, 

 and, as Bennett (1920, p. 353) has pointed out, the dark colour of these whales naturally 

 renders it extremely difficult to see the diatoms unless present in large quantity. 



The Southern Right whale, Balaena australis, has long been protected at all shore 

 stations within the Dependencies. During my stay at the shore station one was captured 

 accidentally in thick weather, but Dr Ommanney reports that no trace of diatom film 

 was observed upon it. 



There are grounds for believing that diatoms may occur both on the Bottle-nose, 

 Hyperoodon rostratus, and the Killer, Orcimis orca (Bennett, 1920, p. 353). Mr G. W. 

 Rayner on a whale-marking cruise during 1929 was able to extend Bennett's observation 

 of the probable presence of film on the latter .species to the South Georgia area. At 

 9 a.m. on January 12, from the catcher 'Petrel', to the south of Cooper Island, a large 

 school of Killer whales was observed moving north-west. Many of them passed very 

 close to the ship, and some appeared to be covered with heavy diatom film. 



The dolphins, Lagenorhyjichm criiciger and Cephalorhynchiis commersom, which are 

 common round South Georgia, where they are known to the whalers as "springers", 

 are thought to become infected at times, and this may well be so, for Mr Rayner has 

 seen them playing round the larger rorquals as they do round the bows of ships. 



Thus it would seem that nearly all the cetaceans found in the seas of the Dependencies 

 are liable to infection with diatom film provided that they remain within the Antarctic 

 Zone for a sufficient length of time. 



Almost any part of the surface of a whale may become infected, including even the 

 surface of the flukes, the umbilical and anal regions. It would appear that the diatoms 

 frequently gain their first foothold, as it were, on old scar tissue. This may in part 

 account for the observation, first made by Mackintosh and Wheeler, that the initial 

 stages in the infection take the form of discrete spots and patches, later coalescing to 

 form the continuous sheet of film. When large portions of the body remain uncovered 

 by film, it is nearly always found that if diatoms are present at all they are in the region 

 of the head, on the rostrum and more frequently on the mandible. Occasionally di- 

 atoms have been observed to penetrate the epidermis, with a markedly deleterious effect 

 upon it, but a bright yellowish colour, observed rarely and superficially indistinguishable 

 from diatom film, appears to be due to some pathological condition unconnected with 

 the diatoms, which were absent from the scrapings. 



THE CONSTITUTION OF THE SKIN FILM 



The vast majority of the diatoms forming the skin film belong to the one species 

 Coccofieis ceticola, Nelson, In the absence of this species two others, C. wheeleri, n.sp., 

 and Navicula, sp. }, have on rare occasions been found to form a film, while several 

 other species were recorded rarely amongst the film of C. ceticola during the 1930-1 

 season. Some were doubtless of accidental occurrence, and it is to be noted that all are 



