NOTES ON THE SPECIES 



257 



/o 



GO 



50 



40 



when large- and small-type diatoms occurred in equal numbers on a few whales. As will be 

 seen later, this was probably correlated with extensive microspore formation in February. 



Observations on the seasonal variation in size of C. ceticola were confined to the 

 1930-1 season when I was able to examine all the scrapings collected myself. Unfor- 

 tunately no observations were made in the October of that year, as the shore station 

 party did not arrive at South Georgia until the end of the month. Large- and medium- 

 sized diatoms predominated over small throughout the season. The maximum for the 

 large size was reached in January and for the medium sized a month earlier. There was 

 a very marked increase in the proportion of small diatoms towards the end of the season, 

 with a corresponding decrease of those of the largest size. 



The most probable explanation of this size variation becomes apparent when we come 

 to consider the life history of C. ceticola. 

 Microspore formation was probably high at 

 the beginning of the season, for as shown in 

 Fig. 2 it was at a minimum in December and 

 January. There was also a very marked increase 

 in microspore formation upon all the classes 

 of whales examined in February and March. 

 These microspores were usually formed in 

 diatoms of the largest size. At first they take 

 the form of small highly refractive spherical 

 bodies with pale green contents arranged round 30- 

 the periphery. Later they appear to take on 

 the characteristic Cocconeis shape gradually, 

 giving rise to small-type diatoms. Presumably 20 

 the larger diatoms are derived from these by 

 auxospore formation, but though ordinary cell 

 division is common I have never been able to 

 detect auxospore formation with any certainty. 

 Auxospore formation is, however, well known 



in the free-living form C./)/«ce«^»/rt(Hustedt, ^^^ ^^^ ^^^ FEB&MAR 



1930, pp. 108, 109), a species which resembles y\^. 2. The seasonal variation in percentage of 

 C ceticola more closely than any of the other whales upon which spore formation of Cocconeis 

 previously known members of the genus. The ceticola was observed at South Georgia in 1930-1. 



„ 1 ,, • .• • .1 1 r • J. Solid line Fin whales, pecked line Blue whales. 



seasonal variation in the number of instances ^ 



in which microspore formation was observed, together with certain observations on 



Sei whales towards the end of the season, enable us to picture the probable way in 



which C. ceticola is disseminated amongst the stock of whales and also furnishes 



important evidence as to the period of time needed for the film to become established 



upon whales after their arrival in Antarctic waters. 



Since C. ceticola has not been observed in any of the samples of neritic or ice diatoms 



so far examined, and as the diatom film is known to disappear when the whales make 



10 







