sea- fisheries laboratory. 373 



Diatoms. 

 It would seem at first sight, from the table given 

 above, that the spring Diatoms compared very favourably 

 as regards numbers with other years, and certainly the 

 maximum is spread over a rather longer period than usual. 

 There were over 4 millions present on two occasions at the 

 end of March, and on July 24th there were over 8 millions, 

 and July 28th nearly 2 millions. But the numbers 

 generally were lower, and the monthly average (nearly 

 27 millions) given for May is rather misleading as, 

 if we deduct the number obtained in two hauls of a single 

 species, the average for the whole month of all the Diatoms 

 is reduced to less than 4^ millions. The species in 

 question is Asterionella japonica, of which 12 million 

 individuals were obtained on May 13th, and 192 millions 

 on May 16th. And this is the more remarkable in that 

 Asterionella japonica is an unusual species to be present in 

 any abundance in our district. The way in which, on one 

 occasion, one species, and on another a different species, of 

 Diatoms appears in great profusion, so as to be represented 

 by millions of individuals in one of our standard hauls, 

 suggests that at a time favourable to the growth and 

 reproduction of spring Diatoms in general, it takes very 

 little to give some slight advantage to one of the numerous 

 competing forms, so that it is enabled to forge ahead, 

 and for a short time, at least, far outnumber all the rest — 

 so as to give rise to what appears as a " Ethizosolenia," 

 or a "Chaetoceras," or, as in this case, an " Asterionella M 

 phyto-plankton. 



The More Important Genera of Diatoms. 

 As in former years, we add here a shorl summary of 

 the distribution throughout the year of the more important 

 Diatoms, 



