20 DISCOVERY REPORTS 



geological history, it is possible that the alien species may have migrated solely by their 

 own capacity to travel, although the powers of locomotion in the Foraminifera are of the 

 poorest kind, so slow as to be almost non-existent. From my own observations I should 

 put an inch in a day as an average limit of active individuals. Many appear to remain in 

 the same position on the sides of an aquarium without movement for days on end, and' 

 of course a great many forms are sessile and cannot move from their environment. 

 Cushman (C. 1933, F, pp. 6-7) gives higher speeds for several species, up to 12 mm. an 

 hour, but the observations were made in the Tortugas, where warmth may stimulate 

 movement. He also gives an average speed of i cm. an hour for Iridia diaphana. 

 Heron- Allen and Earland. But this is a sessile arenaceous form, and the movements 

 were those of the naked protoplasm after the organism had left its test, perhaps in pro- 

 test against detachment from its base, and cannot be regarded as evidence of any normal 

 movement or habit. Upon this observation, which so far as I am aware is the only 

 record of the abandonment of its test by a Foraminifer, Cushman surmises that the 

 animals leave their tests at will, and wander in search of new material to construct a 

 fresh test. The theory has no evidence in its support, except his single observation on 

 specimens artificially removed from their environment, and seems unnecessary, as 

 wave action in shallow waters, and in greater depths the disturbance of sediment by 

 other organisms, would furnish fresh supplies of building material. 



However, given an unlimited time factor, there is no reason why even these "slow- 

 motion" organisms should not travel enormous distances by their own powers and 

 volition, and this may have been the means by which the numerous cosmopolitan species 

 have obtained a habitat in nearly all seas. But the theory fails to explain why these 

 particular forms which we are considering migrated only in an easterly and south- 

 easterly direction, instead of radially from the starting-point, as might have been 

 expected ; unless there was at one time a land barrier which stopped their progress into 

 the central Pacific and confined them to an easterly direction. If geologists confirm 

 such a barrier, the theory of migration by their own power of movement may be 

 accepted as sufficient to meet the facts of the case. 



(3) Transportation by surface currents. These, in the form of the West Wind Drift, 

 are no doubt responsible for the distribution of pelagic species. They account for the 

 presence of Globigerina triloba at many stations right down to the south of the Bellings- 

 hausen Sea. The species was not found by the 'Terra Nova' in the Ross Sea, though 

 Chapman recorded "one specimen" there. Pearcey did not find it in the Weddell Sea, 

 or Wiesner off Kaiser Wilhelm's Land except in one pelagic record. But nearly all 

 Foraminifera are benthic organisms, and cannot be transferred in the adult stage at 

 least by surface currents. Any deep-sea currents are, I take it, too feeble to give 

 assistance. 



Could the Foraminifera be transported by surface currents while still in an immature 

 condition? In the life history of those few species which have been worked out there 

 are two forms, the megalospheric and microspheric, and the megalospheric form 

 generally reproduces by the formation of motile zoospores which conjugate and settle 



