SAG ITT A GAZELLAE 



265 



BOO 6OO 



NORTH 



400 200 AlC ZOO 



NAUTICAL MILES 



6OO BOO 



SOUTH 



IOOO 



Fig. 18. A series of hauls from north-south lines of stations plotted by distance in nautical miles from the Antarctic Con- 

 vergence. The position of the Antarctic Convergence has been determined by reference to the continuous thermograph record 

 from each line. 



VERTICAL DISTRIBUTION 



Fowler's (1898, 1906) method of dividing the water column into three zones, the epiplanktonic, 

 mesoplanktonic and hypoplanktonic is generally used in describing the vertical distribution of the 

 chaetognatha. 5. gazellae, as I shall show, is both epiplanktonic and mesoplanktonic according to the 

 season of the year, and its state of maturity. 



Fig. 19, which has been compiled from the numerical data from 129 vertical stations, shows the 

 average depth distribution of Sagitta gazellae at all seasons in both the Subantarctic and Antarctic 

 zones. Although these vertical hauls (made with the 70 cm. net) can be checked by the deeper oblique 

 nets to determine whether the falling off in numbers below 100 m. is real or due to inaccurate sampling 

 of larger size groups by a small, comparatively slow-moving net, it is not possible to check the 

 difference between the 50-0 and 100-50 m. layers by the oblique hauls, as the shallowest layer 

 normally fished is 100-0 m. Nevertheless, the vertical catches seem consistent. 



The species extends in quite considerable numbers up to the surface, for although the horizontal 

 surface nets have not been systematically examined, occasionally they have been observed to contain 



