188 



Part III. — Sixteenth Annual Report 



each of the three outer stations are those for May and August ; while at 

 Station IV. the highest is that for May, and at Station III. for June; but at 

 Station I. the highest is that for February. The next highest numbers 

 are those for April, May, and August. Some of these points are more 

 clearly indicated by the three formulae. 



Formula (1) shows, as before, the total number of records of Acartia 

 for each of the stations : — 



(a) Inner Stations. [li) Outer Stations. 



Niimbers of the Stations, ... I. III. IV. V. VIII. IX. 



Total number of Records for each Station, 23 26 28 25 23 21 



The station with the lowest number is IX., while that with the highest 

 number is IV., the difference between them being seven. 



Formula (2) shows the total number of records of Acartia for each of 

 the twelve months for the seven years, (a) for the inner stations, I., III., 

 and IV. ; (b) for the outer stations, V., VIII., and IX. ; (c) for all the 

 six stations : — 



Names of the Months, c:.^^'5£j*flii'^&,^^*o 



T^foi ^„r..w of r (*) the Inner Stations, - 0 9 2 11 11 11 5 10 4 6 7 1 

 Sfcords ?or each (^) '^'^ Outer Stations, - ^ ^ ^ 1^111 11 



Month, for y g.^ Stations, - 0 14 4 18 24 16 10 25 9 12 12 2 



If these figures be closely examined and compared, it will be found that 

 there is a more or less evident maximum in the total number of records 

 about every three months. This is also found to be the case, though not 

 so distinctly, when the numbers are divided so as to correspond with the 

 inner and outer stations. But taking the total numbers first, it will be 

 observed that, commencing with February, the total number for which is 

 fourteen, there occurs in March a sudden drop, after which the numbers 

 increase till May, when the second highest total for the whole year is 

 reached. In June and July the numbers again fall, to be followed by a 

 marked accession in August, so much so that the maximum for all the 

 twelve months occurs then ; in September there is again a marked 

 decrease, after which a slight recovery takes place in October and Novem- 

 ber, while in December the number is, next to January, the lowest for 

 the year. This increase and decrease, though not so apparent where the 

 numbers are divided to correspond with the inner and outer stations, can 

 still be traced, especially in the series corresponding to the outer stations. 

 The reason for this apparent rhythmical arrangement is not very clear, 

 and it may be that the seemingly periodic recurrence of Acartia may be 

 merely accidental. 



Formula (3) shows the total number of records of Acartia for each 

 year, for (a) the inner stations, I., III., and IV. ; (b) the outer stations, V., 

 VII J., and IX. ; and (c) all the six stations : — 



Numbers of the Years, - - - - - 1889. 1890. 1891. 1892. 1893. 1894. 1895. 

 Tn+oi ^^.rr.y.^r. of ( I^i^^r Statious, - 4 10 24 16 14 5 4 

 Rto^fac^^^^ 1 1 ^1 '1 1 1 1 



[ (c) all the Six Stations, - 8 23 49 29 19 9 9 



It will be observed that the maximum number — that for 1891 — is pro- 

 portionally considerably greater in comparison with the others than is 

 observed either in the case of Calanus or Temora. 



A few of the other species of Copepoda referred to in the lists of tow- 

 net invertebrates, such as Pseudocalanus elongatus, Centropagus sp., 

 Anomalocera patersoni, and Oifhona sp., are also at times more or less 

 frequent in the Firth of Forth, but the published records of them show 

 that they are usually less common than those already noticed. 



