250 DISCOVERY REPORTS 



throughout the season. From February onwards thick films covering a large part of the 

 body were sometimes recorded, and conditions are known to be favourable to rapid 

 growth at that time. Immature whales were usually found to be free from film, but 

 patches were found upon them during the later months of the season. The extremely 

 interesting observation that small spots of diatom film occurred on a few immature 

 whales at Saldanha Bay, South Africa, during the winter months of August and 

 September, was also made. The larger mature whales taken at this station were entirely 

 free from infection. This is in good agreement with Bennett's conclusion that the skin 

 film is acquired in Antarctic waters. It may now be considered as well established that 

 a majority of the immature whales lag behind the larger mature whales on their south- 

 ward migration (Harmer, 193 1, pp. 107, 108), and it is therefore almost certain that 

 their return to warmer waters is similarly belated. 



Mackintosh and Wheeler noted that early in the season at South Georgia what 

 appeared to be initial stages in the formation of diatom film were frequent. These 

 took the form of small round green patches on the skin an inch or so in diameter. 

 From the conditions observed later it appeared that these were growing colonies 

 which expanded gradually from numerous centres and eventually covered perhaps 

 the whole body within a few months. 



In addition to these published works, notes on the diatom film have been made from 

 time to time in the official reports of the officers engaged in the study of whales, which 

 I have been able to consult. Acknowledgments of these sources of information are 

 made in appropriate sections of this paper. 



MATERIAL AND METHODS 



My own opportunities for direct examination of the skin film were confined to a few 

 visits to the plan at Grytviken, South Georgia, during the 1 930-1 season, as I was 

 principally engaged on other work during my stay at the Marine Biological Station. 

 During that season, however, all the scrapings were brought to me for microscopic 

 examination. I have also examined fifty-six scrapings collected by Mr A. H. Laurie 

 on board the S.S. ' Southern Princess', when the vessel was working pelagically in the 

 Indian Ocean sector of the Antarctic during 1932-3. Mr Laurie was working single- 

 handed, so that it was quite impossible for him to make full external examination of 

 all the whales captured. This collection, small as it is, has proved most valuable for 

 comparison with material from the Atlantic sector. 



The rest of the material upon which these observations are based consists of notes entered 

 in the whaling logs kept by the Discovery staff for the following seasons and localities : 

 1928. January 16-27. Deception Island, South Shetlands ... 29 whales 

 1928-9. Grytviken, South Georgia ... ... ... ... 776 whales 



1929-30. Grytviken, South Georgia ... ... ... ... 725 whales 



The following officers were responsible for the collection of these data : 



1928-9. Mr F. C. Fraser, Mr J. W. S. Marr and Mr G. W. Rayner. 

 1929-30. Dr J. F. G. Wheeler and Dr F. D. Ommanney. 



