SAGITTA GAZELLAE 263 



likely that the Tonga specimen was not S. gazellae. In the Revision of the Chaetognaths ( 1 9 1 1 ) he states 

 that the distribution of S. gazellae is between 6o° and 66° S. in the Antarctic, and that the most 

 northerly catch was 35-5° S. He also states that it occurs in deeper water farther north; but I think 

 this last statement is a reference to the catch from 35-5° S. rather than a suggestion of tropical 

 submergence. 



Subsequent records are mainly from Antarctic and Subantarctic waters, but there are a few 

 exceptions. 



Burfield (1930) records S. gazellae from Rio de Janeiro (23 S.) from the 'Terra Nova' hauls, but 

 on p. 219 of his report remarks 'The horizontal range of the stations at which this form was captured 

 extends from lat. 23 N. to lat. 77 38 S.\ From the station numbers and distribution charts, it would 

 appear that 23 ° N. is a misprint, and should be 23 ° S. Through the kindness of the British Museum 

 (Natural History) I have been able to examine the original ' Terra Nova ' hauls from Rio de Janeiro 

 (Stations 39 and 40) and, although the specimens are in a bad state of preservation, it is evident from 

 the position and shape of the seminal vesicles that they are S. enflata and not S. gazellae. 



Tokioka (1939) records S. gazellae as a synonym of S. lyra in Japanese waters, but these specimens 

 are almost certainly the cold water form of S. lyra. 



Thomson (1947) found S. gazellae in Tasmanian waters, but followed the synonymy proposed by 

 Johnston & Taylor (1921) and Tokioka (1939) and described them as S. lyra. The Discovery collec- 

 tions from Tasmanian waters contain specimens of S. gazellae, and their presence there may be due 

 to vagaries of the subtropical convergence. 



Furnestin (1953) reports S. gazellae from the Mediterranean, but has informed me that, after 

 reading a typescript copy of part of this paper, she considers them to be S. lyra "gazellae "-type. 



Table 13 a gives the numerical data from 496 shallow oblique hauls. The year has been divided into 

 four equal seasons, and the table is in two parts, one for the Subantarctic, and the other for the 

 Antarctic zone. 



The difference in size of the population for the two zones is immediately apparent, the average for 

 165 Subantarctic samples is 120-3 per 20-minute haul, as compared with 27-2 based on 331 Antarctic 

 samples. 



The striking decrease in numbers in the upper layers during the winter months is evidence of a 

 seasonal migration, comparable with that described by Mackintosh (1937) for certain other Southern 

 Ocean plankton species. 



Though in the Subantarctic the total for August is rather exceptional owing to a single haul at 

 Station 2869 of 502 individuals, three other hauls made at different times of the year in almost the 

 same position (in the vicinity of the Crozet islands) all yielded very large numbers, and the presence of 

 S. maxima in quite large numbers at the surface in this area suggests that some exceptional conditions 

 exist there. The haul at Station 2869 is the only August haul in the collections which contains large 

 numbers of S. gazellae, and if it is omitted the average for August becomes 48-0, and the winter average 

 66-3 ; these figures (shown in brackets in Table 13 a) give a more accurate picture of normal conditions. 



The Subantarctic winter average is low because a part of the population is at a depth of more than 

 100 m. In spring the average increases with the return of most of the population to the surface. The 

 summer average is the highest owing to the appearance of young individuals at the surface. In autumn 

 the average decreases for two reasons, the commencement of the winter vertical migration in April 

 and May, and the extensive migration in March and the beginning of April in which the larger size 

 groups of the population descend to the deeper layers to mature and breed. However this decrease is 

 to some extent offset by the appearance in the surface layers in May of young from the March April 

 breeding period. 



