28 PROCEEDINGS OF THE 



with its wider range through the deeper layers o£ water, gave a 

 larger and sometimes a much larger quantity of organisms. The 

 only exceptions to this rule are on some occasions in April, when 

 the sea was full of Diatoms and the surface-nets gaye very large 

 hauls, equal to or even exceeding the deeper ones. But even 

 during the Diatom maximum in April some days showed more 

 in the weighted than in the surface-nets. For example, on 

 April 10th, at along-shore station III, the surface gave 11-5 and 

 the net at one fathom 19'5 c.c, and the total Diatoms were 

 27,000 in the former and 188,000 in the latter. 



In some cases, as I showed last year, the two similar surface- 

 nets worked together gave dissimilar results. Even when the 

 results are very much alike quantitatively, they may be very 

 different qualitatively ; and it is by no means always the two 

 hauls that are most alike in bulk that agree best in the kind 

 and number of organisms. It will probably be agreed that it 

 is unlikely that, with the large, varied and irregularly scattered 

 population that we jfind the sea to contain, two nets should 

 often catch the same quantities of the same sets of organisms. 

 Consequently a result like that obtained on April 22nd, where 

 the two nets caught precisely the same amounts and where the 

 lists of organisms constituting the hauls are almost exactly alike 

 both in kinds and numbers, is interesting. 



On considering the Diatom list, some other points come out : — 

 The average number of Diatoms per catch often varies considerably 

 from day to da v. Thus on April 5th the average of all catches of 

 that day was 3,533,800, while on April 6th it fell to 348,750 ; 

 on April 24th it was 191,873, while on April 25th it was only 

 663. 



But these numbers scarcely give an adequate idea of the 

 quantitative variation among individual catches. Thus on 

 {September 10th surface-nets A and B contained 250 and 550 

 respectively, while two days later the corresponding numbers were 

 13,495,500 and 16,300,500; on April 8th two hauls of the 

 JSTansen net gave respectively 198,000 and 3,739,000, and many 

 other such cases could be quoted. 



A general inspection of an uusmoothed curve drawn from the 

 list of Diatom hauls within Port Erin Bay, shows a well-marked 

 maximum at the end of March and earlier part of April. The 

 marked increase of Diatoms, and also of Copepod Nauplii, towards 

 the end of March is seen well in the following three surface 

 hauls : — 



March 26. March 27. March 29. 



12 c.c. 145 c.c. 18o c.c. 



Total Diatoms = 220,000 ... 277,000 ... 326,000 



Biddulphia mobiliensis 46,000 ... 50,000 ... 58,000 



Chffitoceros debile 6,000 ... 8,000 ... 10.000 



decipiens 100,000 ... 150,000 ... 160,000 



Coscinodiscus eoncinnus 64,000 ... 67,000 ... 75,000 



Oopepod Nauplii 7,000 ... 27,000 ... 35,000 



There is also an autumn maximum in the Bay showing a very 



