CORRELATION WITH FATNESS 279 



thirdly, that, as in the previous year, while some of the January immature arrivals 

 undoubtedly came from the north, many of the later ones had been within the Antarctic 

 Zone for a considerable time, and probably came from the westward. It may be thought 

 that the opinion derived from diatom data, that some of the January immature arrivals 

 came from the north, is inconsistent with the observation that the average condition 

 of the total Fin whales taken during that month showed an improvement on the 

 December figures, but the altogether exceptional poverty of the latter, and the still 

 moderate proportion of immature whales in the January catch, render this objection 

 untenable. The condition of the Fin whales in December of this season was indeed 

 considerably poorer than in any of the other month groups studied, and if the solid 

 lines in Figs. 7 and 8 are compared, it will at once be seen that from November onwards 

 the condition of the whales taken in 1929-30 was appreciably poorer than that of those 

 captured during the previous season. This is in striking agreement with one of Bennett's 

 observations at the South Shetland Islands, quoted by Harmer (1931, p. 107), that 

 during "big Fin whale years" the condition of the whales tends to be poorer than 

 usual. The season 1929-30 was a big Fin whale year at South Georgia, the proportion 

 of Fin to Blue in the total catch being more than five to one, as against a proportion 

 of less than two to one during the previous season, as may be seen from the figures 

 given in Table I. 



The considerations set forth at length in this section seem to justify the conclusion 

 that, with rare exceptions during the early part of the season. Fin whales heavily infected 

 with diatoms tend to be in better condition than the average oflF South Georgia, a fact 

 which is recognized by the whalers. Some of Mr Rayner's observations on whale- 

 marking cruises show that at times when large schools of Fin whales are feeding 

 together in calm weather it is quite possible to distinguish the film, when extensive, 

 from the decks of a catcher. It follows that, by selecting the heavily infected whales, 

 the gunners could render their companies good service, and at the same time avoid 

 wastage of the stock by slaughter of immature whales, which as we have seen are rarely 

 heavily infected before the last month of the season. Unfortunately such ideal con- 

 ditions are very rare on southern whaling grounds, but when they do occur there 

 seems little doubt that the gunners endeavour to exercise this discrimination. 



SUMMARIZED CONCLUSIONS 



The first part of this paper consists of an account of the occurrence of diatoms in the 

 cutaneous investment of cetaceans in Antarctic waters. Though commonest upon Blue 

 and Fin whales, there is evidence that diatom film may occur on almost all the species 

 of Cetacea known to inhabit these seas. Besides the usual "skin film" form, Cocconeis 

 ceticolo. Nelson, two other diatoms have been observed in quantity sufficient to form 

 film visible to the naked eye on rare occasions. These were a small indeterminate 

 species of Navicula, seen on Blue, Fin, and Sperm whales, and Cocconeis wheeleri, n.sp., 

 found only on Humpbacks, and named after its discoverer, Dr J. F. G. Wheeler. Besides 

 these species, several diatoms have been found in the skin film that are thought to be 



