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PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



The large islands off the coast of southern California 

 have all the characters of continental islands. They 

 have been separated from California in comparatively 

 recent times. The flora of these islands is very peculiar. 

 Out of three hundred species described, at least fifty 

 are found nowhere else. The others are similar to 

 those in California. But in the California flora it is 

 necessary to distinguish two groups — viz., a distinctively 

 Californian group and a group which is more widely 

 diffused. The former I shall call indigenes or natives ; 

 the latter are probably invaders. Now, it is the distinc- 

 tively Californian group only that is found on the islands. 

 These are the facts. Now the 



Explanation. — Before the glacial epoch the islands 

 were a part of the mainland and all had a common flora 

 — viz., the group I have called indigenes. Then came 

 the separation by subsidence and the isolation of many 

 indigenes on the islands. Then came the glacial cold 

 and the invasion of California by a northern flora, the 

 struggle between invaders and natives, the destruction 

 of some native species, and the modification of both na- 

 tives and invaders by new environment and by conflict. 

 The final result was the California flora of to-day. The 

 island flora was spared the invasion and the conflict. 

 It has been changed less than the native Californian. 

 We have in them a nearer approach to the preglacial 

 flora of both. 



7. Oceanic Islands and their Fauna. — Oceanic islands 

 are built up from the sea bottom mostly by volcanic 

 action, and have never had any connection with a conti- 

 nent. We see these forming now. When first formed 

 they are, of course, uninhabited. They receive their 

 species, animals and plants, as gifts from the sea— mere 

 floating waifs brought by waves and currents. Their 

 fauna and flora are always peculiar because isolated, 



