DISTRIBUTION OF THE CHAETOGNATHA 219 



species. It can also be seen from these sections that there are two populations oi S . gazellae , representing 

 the two races which occupy respectively the antarctic and subantarctic surface waters, while to the 

 north S. serratodentata (see Fig. 10) occupies a similar habitat in the subtropical zone. In the deeper 

 layers S. marri, S. maxima and S. decipiens (see Fig. 11) are distributionally analogous in the three zones. 



LATITUDE 



STATION 

 50 

 100 



250 



'2 500 



X 



a 750 



a 



1000 



2025 2024 2Q23 



AC 

 2022 



STC 



* c 

 4,0-= 



2802 2803 2804 



AC 



5,0"S 

 2805 2806 



1500 



LATITUDE 



B 



Fig. 10. The vertical distribution of S. serratodentata in 0° (A) and 90° E(B). 



STC 

 ^ 4,0° 



AC 

 50° 



STATION 2027 2026 2025 2024 2023 2022 



4V 



AC 



5,0°S 



I 

 I- 

 a. 



UJ 



2802 2803 2804 2805 2806 



-1 1 I L 



I500 



B 



Fig. II. The vertical distribution of S. decipiens in 0° (A) and 90° E (B). 



This rather striking segregation of the species of Sagitta is of considerable interest, for although 

 mixing does take place, there is no doubt that each species is concentrated in a particular area to the 

 relative exclusion of the others, and it must be presumed that minor differences in the physical 

 characteristics of these water masses are responsible for the segregation of the species, for reference to 

 the temperature/salinity diagrams shows that most of the species can tolerate a greater range than that 

 in which they are most abundant. This segregation must have been of considerable importance in 



