194 THE ZOOLOGIST. 



several ways in which species of animals can be supposed not 

 only to have reached the broinelia-marsh in the past but also 

 to reach it still from time to time. Some minute kinds, such 

 as Copepods and Rotifers, could be transported in the form of 

 eggs or cysts by wind. In steep places mud and water, perhaps 

 containing living things, may often be splashed over the boughs 

 of trees by landslides. Many species also have doubtless colonised 

 the plants by active migration. Some would take to frequenting 

 bromelias in order to derive a living from them, either directly 

 or indirectly, in the manners indicated at the close of the 

 preceding section. Others may resort to them in order to escape 

 the evil effects of drought. This may be the case with Snails, 

 Planarians, and Earthworms. In the Seychelles a Land- 

 Nemertean and a Land-Leech were found sometimes in damp 

 places on or near the ground, at other times between Pandanns 

 leaf-bases ; is not the moisture possibly the attraction of the 

 latter situation ? In India, too, certain Oligochset Worms have 

 been found in hollows half full of water in tree-trunks, whither 

 they resort on the drying up of their habitats on the ground ; 

 it is stated that they have been observed in the very act of this 

 migration. As to creatures such as Dragonflies, Caddisflies, 

 &c, it is not hard to imagine that, if they wandered in their 

 flight far into the depths of forests and found there no terrestrial 

 waters, they might lay their eggs in the only available water — 

 that in the reservoir-plants. 



All this does not explain the origin of exclusively bromelicolous 

 species. But is it not conceivable that if some individuals of a 

 species became established in the bromelias, and that if their 

 ranks were not frequently reinforced by the arrival of others of 

 the same species from without; that then they and their descen- 

 dants might be affected by the isolation in so special a habitat, 

 just as some other forms are affected by becoming restricted in 

 their habits to special food-plants or in other ways ? Might not 

 modifications occur, culminating in the forms affected becoming 

 so distinct as to be regarded as separate species?* 



:: For a discussioQ of isolation and segregation of forms due to difference 

 of habits, see the highly suggestive " Introductory Essay on the Hawaiian 

 Fauna," by Dr. R. C. L. Perkins, recently published in ' Fauna Hawaiiensis ' 

 (vol. i., part 6, 1913). Perkins lays the greatest stress on isolation as a 



