PATCHINESS 263 



some extent serve as a "control" experiment in relation to the single hauls at isolated 

 stations. Vertical hauls with the N 70 V closing net were made from the bottom to the 

 top in the following series: 265-1 50 m., 150-100 m., 100-50 m. and 50 m. to the surface, 

 and whilst the experiment could not be continued as planned for the whole 24 hours 

 due to an oncoming gale, the series was repeated five times during a period of 8 hours 

 at 1300, 1540, 1700, 1910 and 2105 o'clock respectively. We shall consider the 

 differences in the total numbers of the different organisms taken in the whole vertical 

 column from the bottom to the top, so that these differences will be quite independent 

 of changes due to the vertical migration (unless some organisms are actually resting for 

 part of the time on or within a few feet of the bottom). We shall express the total num- 

 bers as numbers per 50 m. haul, so that they will be comparable with the similar numbers 

 we have used for the different organisms in charting their distribution in the upper 

 250 m. round South Georgia. 



SUN MID SUN 



SET NIGHT RISE 



fWTH OF NETS 



-oo-crew-e-e - Oo q q 



Fig. 136. 



Since the nets used for each series were exactly the same and used in exactly the same 

 way, the differences in the numbers recorded are due either to the working error in the 

 laboratory analysis or to actual differences in the concentrations sampled by the net, 

 i.e. to unevenness in distribution of the species concerned in the water drifting past 

 the ship at anchor. The range of the error in laboratory analysis has already been 

 determined and discussed on pp. 30-38, so that the unevenness in distribution of a 

 particular species may be gauged by the extent to which the range of difference in 

 numbers found exceeds the determined range of error in laboratory methods. 



The results obtained are shown in Table XLVI. 



Four species Ctenocalanus vanus, Drepanopus pectinatus, Oithona frigida and Oncea 

 notopus show a range of variation in numbers far exceeding the range of laboratory error, 

 and may be said to display distinct patchiness within a small area, i.e. the area of drift 

 past the ship between 1300 and 2105 o'clock. The degree of patchiness of these four 

 species is shown in Figs. 137-140, where the excess of variation in numbers over the 

 possible range due to laboratory error is shown. 



We have already seen from the consecutive net series that C alarms propinquus tends 

 to occur in much larger patches, so that we should not expect a marked patchiness 

 in a small area as sampled at St. 41. A general idea of the larger patchiness of various 

 species may be gained by the study of the vertical distribution figures for the South 

 Georgia survey December- January 1926-7. Scolecithricella minor, which is all but 

 absent from St. 41, shows a marked patchiness when the line of five stations 13-17, 

 taken at ten-mile intervals off the north-east coast of South Georgia in March 1926, is 

 considered. The average number per 50 m. haul for the top 250 m., taken at these 

 stations in order from 13 to 17, is as follows: 7, 324, 5, o and 434. 



34-2 



