SWARMING OF THE GRIMOTHEA STAGE OF M. GREGARIA 243 



was made independently and in complete ignorance of Young's observation on the same 

 phenomenon in New Zealand waters in 1925. His description runs: "The smaller 

 shoals often take a circular shape like a swarm of bees, and the incessant motion of each 

 individual tends to heighten the illusion ". 



On February 17, 1932, whilst the R.R.S. 'Discovery 11' was lying at anchor in Port 

 Stanley Harbour, a shoal of Grimothea came alongside the vessel during darkness and 

 was seen in the water by the light of the gangway cluster lamp which seemed to be an 

 attraction. In the laboratories of the ships the Grimothea stage has been observed to 

 display a strong positive heliotropism. The light from a hand torch would cause them 

 to back towards it with remarkable rapidity and precision. On the other hand, on 

 May 23, 1926, specimens were taken in horizontal tow-nets used at depths down to 

 90 m. at Sts. 66 and 67 which do not corroborate this. St. 66 was made in the dark 

 hours, and specimens were obtained at the surface, at 45 and at 90 m. St. 67 made 

 during daylight hours yielded specimens at 45 and 90 m. On both occasions the largest 

 catches were in the deepest nets. The degree of heliotropism, should any exist, in the 

 pelagic form of M. gregaria may vary according to the stage in development, and a 

 specimen positively heliotropic in February might exhibit a very different reaction to 

 light in May. 



The swarm of M. gregaria from which the specimens obtained at Sts. 66 and 67 were 

 taken was evidently being swept away from suitable and favourable habitats. It was 

 already 300 miles from the nearest land in water of a greater depth than 4000 m. and 

 under the influence of the Falkland current which would continue to carry it to the 

 north-east. It has been shown that M. gregaria is a shallow coastal water form, and it 

 would seem that individuals of a swarm such as this, which had been swept away from 

 the adult habitat, would fail in the normal fulfilment of their life history. 



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