SAGITTA GAZELLAE 271 



been compiled from ninety-three vertical stations, the number of individuals at each stage of maturity 

 being expressed as a percentage of the total numbers in each horizon. Both races of S. gazellae are 

 combined and the stations are from nearly all months of the year. It can be seen that in the deepest 

 hauls (1 500-1000 m.), the mature stages III and IV represent more than 50% of the total. 



Stage I is the commonest in the 100-50 m. layer, though the difference in percentage composition 

 in the three shallow layers is small. 



Stage II reached a maximum in the 750-500 m. layer, falling off above and below this level. 



Stage III appears in the 1000-750 m. layer, being as numerous as stage II at that depth. 



Stage IV appears in the 1500- 1000 m. layer, but is not as numerous as stage III. 



Table 14. Vertical distribution of mature specimens from closing nets 



(S.N. race, light type; L.S. race, heavy type.) 



Table 15. Vertical distribution of all stages at ninety -three stations — each stage given a 

 percentage of the total for each depth (percentages in heavy type) 



GROWTH RATE AND LIFE HISTORY 



The seasonal vertical migration of S. gazellae, in which part of the population sinks below the horizon 

 of the shallow oblique nets in winter, is the main factor which makes a study of the growth rate of the 

 species possible. In summer months the range of size groups in the population is so great that it is not 

 possible to identify, or follow the progress of, one particular brood among all the others. In winter, 

 however, one brood is left within the horizon of the shallow (100-0 m.) oblique nets, and its progress 

 can be observed from May when it first appears until September and October when it becomes mixed 

 with other broods, and its individuality is lost. This, however, applies only to the Subantarctic zone, 

 for in the Antarctic the seasonal migration carries the population almost entirely below the horizon of 

 the shallow oblique nets, and in addition the ice conditions prevent a study of the southern part of 

 the Antarctic zone during the winter months. Thus the growth rate and life history of the L.S. race 

 can only be inferred from that of the S.N. race. 



