SAGITTA GAZELLAE 275 



due to the greater number of deep towed nets fished in this month and hence the larger quantity of 

 specimens available. The N70V net, though it obtains specimens in perfect condition, catches only 

 a few of the smaller Subantarctic race, and it catches still fewer specimens of the large Antarctic race. 

 The large deep-towed nets, which are the main sources of supply of specimens of the mature L.S. race, 

 have not been regularly fished, and so no real indication of the frequency of breeding can be obtained 

 from the catches of mature animals. 



Very large individuals (>9omm.) are found in the Antarctic zone; these are apparently non- 

 breeding (Fig. 27), and are usually found at the surface in winter and spring; they do not appear to 

 perform either a seasonal or a breeding migration. They are never found at a more advanced stage of 

 maturity than stage II, and the largest specimen taken to date measured 105 mm. (fresh). This is 

 probably not the largest, for preserved specimens of 99 and 100 mm. have been examined on several 

 occasions, and taking shrinkage into account (see p. 240) the maximum length fresh is probably 

 108-110 mm. It is possible that in certain cases individuals have not been able to migrate to breed 

 because they have been in shallow water, and have therefore continued to feed and grow at the surface ; 

 the large specimen of 105 mm., for example, was taken at Station 1007 where the sounding was only 

 152 mm. However, in many cases these large animals are found over deep water, and one must assume 

 that there is another factor which operates to prevent both breeding and seasonal migration. 



FOOD 



S. gazellae is frequently taken with animals held in its jaws, but this is not necessarily any indication 

 of its normal food, for often the animals which it has seized are far too large to be ingested — large 

 medusae or fish for example — and not infrequently specimens are found which have bent back upon 

 themselves and seized their own tails. While a net is being hauled the animals concentrated in the net 

 bucket are swirled together, and evidently S. gazellae will seize anything it touches ; during fixation 

 also, the animals make convulsive movements which may have a similar result. 



Observations have been made of specimens with food in the gut, and owing to the great trans- 

 parency of the animal it has sometimes been possible to identify the species of food animal. These 

 positive observations are however surprisingly few. In two commissions of 'Discovery II', during 

 1931-33 and 1950-51, only in forty-five hauls out of 667 examined were specimens of S. gazellae 

 recorded with food in the gut; this does not mean only forty-five specimens, for in many cases there 

 were a number of animals with food in their gut found in one haul, but even so the number is 

 very low. 



Table 17 shows that Copepods and Euphausians are the commonest food animals for the species, 

 the third group, Chaetognaths, being but 13% of the total. 



No mature S. gazellae has been found with food in the gut, but the total number of matures taken 

 is small, and this may therefore be of no significance. 



On one occasion a large specimen of S. gazellae was kept alive aboard ship for nearly 2 hours, and 

 was given a live Euphausian to eat. The food was touched against the mouth of the chaetognath which 

 promptly seized it and pushed it into the mouth by alternate movements of the hooks on each side ; 

 once in the mouth the food was passed rapidly down to the middle of the gut, this process taking about 

 10 minutes; from this point to the posterior end of the gut the passage of the food was much slower, 

 and it reached the posterior end about 1 hour after ingestion. The animal died before it had defaecated. 

 The behaviour of one specimen in far from natural conditions must of course be regarded with 

 reserve. 



Chaetognaths form part of the diet of many marine animals, notably of fish. Large pelagic fish are 



