of the Fishery Board for Scotland. 193 



number of the records for each of the twelve months, it will be observed 

 that those for February and December are considerably greater than the 

 numbers for the other months ; but if the numbers are separated into two 

 groups to correspond with the inner and outer stations, the difference in 

 the numbers for each of the twelve months for the three inner stations is 

 increased, while the difference becomes less in the other group of numbers. 

 This is best seen by arranging the numbers as a formula. 



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

 the twelve months, for (a) the inner stations, I., III., and IV. ; (b) the 

 outer stations, Y., VIII. , and IX. ; and (c) for all the six stations : — 



Names of the Months, - - a % £ & £ % S g> A £ > g 



m , . . f f{a) the Three Inner Stations, 19 30 10 16 15 7 9 11 6 14 19 24 



lotal number ot , {b) th Th 0ut Stations 18 30 io 18 21 17 19 17 15 20 17 26 



Records for each*; x ' ' 



Month, for [^ all the gix StationS) . 37 60 20 34 36 24 28 28 21 34 36 50 



There is one point very clearly brought out in connection with the dis- 

 tribution of the Sagitta — viz., that, whether a comparison be made of the 

 monthly numbers of records for each station or for the three inner and 

 three outer stations or for them all, the numbers for February and most 

 of those for December are greater than the others. This would seem to 

 indicate that Sagitta was usually more common during these months than 

 at other times of the year. 



It will be further observed that the highest total number of yearly 

 records, viz. 79, is that for 1892, and the smallest, 31, for 1894, and that 

 if the yearly records be divided into two sets to correspond with the three 

 inner and the three outer stations, the results, as regards the highest and 

 lowest numbers, arc somewhat different. In this arrangement of the 

 figures the highest number for the three inner stations is that for 1893, 

 and the lowest that for 1889, while the maximum and minimum numbers 

 for the outer stations are for the same years as in the former arrangement. 

 Formula (3) will show these results more clearly. 



Formula (3) shows the total number of records of Sagitta for all the 

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

 stations, V., VIIL, and IX. ; and (c) for all the six stations : — 



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



„ , . , - / (a) the Inner Stations, 13 26 34 33 36 18 20 



Records foreach < ^ the 0uter Stations > 24 33 40 48 42 13 25 



Year, for ( ( c ) a n the Six Stations, 37 59 74 81 78 31 45 



It would thus appear that Sagitta, like the majority of the other 

 pelagic organisms of which there are records, are usually of more frequent 

 occurrence in the Firth of Forth and its vicinity during the colder months, 

 and that they were more numerous during 1891, 1892, and 1893 than 

 during the other years. These again coincide with the yearly maxima for 

 Parathemisto, and may be the result of a larger migration during these 

 years, as was probably the case with Parathemisto, or to circumstances 

 favouring a greater local increase ; for though the difference in the 

 number of the yearly records may be partly accounted for by the greater 

 or fewer number of experiments, this does not explain the whole of it. 

 Unfortunately the experiments were not carried on long enough nor so 

 regularly as to indicate whether the difference shown is due to the actual 

 increase or decrease of these organisms, and whether it was temporary and 

 accidental or part of a more or less regular cycle of changes in their 

 migration or development. 



