THE CONSTITUTION OF THE SKIN FILM 



255 



one of the dominant forms in the bottom deposits round the island. Hence it might 

 well be argued that its presence upon the whales was accidental. The following con- 

 siderations, however, support the view that it may be a true constituent of the skin 

 film. In the first place, of all the littoral forms it is perhaps the least frequent in the 

 inshore plankton, doubtless on account of its heavily silicified frustules; and in the 

 second, while the individuals upon the kelp were very variable in size and in the number 

 of costae, those seen upon whales were markedly uniform in size and invariably had 

 twenty-six costae on either side of the raphe. The endochrome of the individuals seen 

 upon whales was generally pale green in colour, while that of those upon the kelp was 

 yellowish brown. The formation of microspores of this species was observed among the 

 individuals found on whales, but not among those from other habitats. It was frequent 

 upon freshly killed whales, and although known to occur on the kelp near the whaling 

 station no increase in its numbers was ever noted upon whales left lying a long time in 

 the water before flensing, doubtless owing to the almost complete absence of the 

 tychopelagic habit in this species. It would seem, therefore, that in the vicinity of South 

 Georgia C. imperatrix may be a true constituent of the skin film. 



C. gautieri, first described from bottom samples from the Antarctic Zone, and later 

 recorded from the southern sea-ice, was not o- 

 observed at South Georgia except upon whales, cq 

 C. imperatrix is also known as an ice form, 

 and here we have a probable source of the 

 infection of South Georgia whales by these 40 

 two species during the early part of the 1930-1 

 season. The ice at that time lay unusually far 

 north, and undoubtedly led to a local accumu- 30 

 lation of whales, some of which would normally 

 have proceeded farther south, particularly the 

 Blue whales. As shown in Fig. i the percentage 20- 

 of whales upon which species other than C. 

 ceticola were observed fell steadily throughout 

 the season, and was particularly high during 

 the first month. While it is possible that some 

 of these diatoms, such as Lycmophora lyngbyei, 

 were acquired during the whales' southern 

 journey, in littoral south temperate waters. 



NOV DEC JAN FEB K MAR 



Fig. I . The monthly variation in the percentage 



perhaps off the Patagonian coast, the sea-ice °^ '^e total Blue and Fin whales upon which 



, , ,11 r , "other Species" were observed during iQio-i. 



appears to be the more probable source or the 



infection, particularly with regard to Cocconeis imperatrix and C. gautieri, which are 



known to occur upon it. 



Various minute species of Navicula have been observed from time to time in the skin 



film in numbers such that their occurrence can scarcely be regarded as fortuitous. Their 



specific identification is a matter of extreme difficulty owing to the chaotic state of the 



