152 ANIMAL ECOLOGY 



When palaeontologists speak of the migration of animals 

 into a new country, they usually have a vague idea of some 

 species like the caribou walking from its original home in a 

 large crowd, and arriving in force at the destination. What 

 probably happens is rather the process described above, which 

 is a great deal less spectacular and lasts over a very much longer 

 time. Big-scale migrations do exist and of course attract 

 attention from their very size, but it cannot be too much 

 emphasised that the spreading of species is, in ninety-nine 

 cases out of a hundred, a slow process intimately bound up 

 with the local habits and habitats of the animals, and with 

 ecological succession. 



6. Among many animals the daily migrations in search of 

 food and other necessities are more or less regular and well 

 defined. Crozier^^* observed an amusing case of this sort 

 among the molluscs of the coast of Bermuda. He found that 

 Chiton tuberculatus (a species about nine centimetres in 

 length) does not wander very far frond its *' roosting-place," 

 but travels within about a radius of a metre from its home. 

 One individual which was observed had a small Fissurella 

 (length about 0*9 cm.) living on it, browsing upon the 

 epiphytic growths which covered the valves of the Chiton, 

 The Fissurella also wandered about all day over the Chiton^ 

 but always returned in the evening to the third valve ! 



Seasonal migrations of a regular nature occur among many 

 animals besides birds. (For an up-to-date account of bird 

 migration the reader may be referred to A. Landsborough 

 Thomson's Problems of Bird Migration,^^^ since the subject 

 is far too large to be adequately dealt with here.) Instances 

 which will immediately occur to the naturalist are the migra- 

 tions of fish in search of their spawning grounds, or of herbi- 

 vorous mammals in search of pasture. In Palestine a certain 

 amount of excitement and discomfort was at one time caused 

 by large numbers of migrating scorpions, which invaded the 

 military camps that happened to have been planted in their 

 path. In the same way it has been noted ^^^ that the common 

 bandar or rhesus monkey and the Hanuman monkey of India 

 trek in parties (formed of a mixture of the two species) from 



