DISPERSAL OF SPECIES. 21 



working tlio organic impulses which produce organic changes. It is, I imagine, analogous to 

 the physiological phenomena which occur in our own bodies in health and sickness, especially 

 as seen in the weak and aged. So long as we go on in our regular daily course of life, we enjoy 

 our usual health. Some trifle occurs to disturb this regularity. We say we are upset by it. We 

 are jolted off the rail ; the doctor tries to get us back into the old track, but the impulse of change 

 has been set a going, and the system instead of returning into its old groove sets off in a different 

 direction, vires acquirit eundo, and when he asks for us to-morrow we are grave men. It may 

 bo that particular conditions produce particular effects, as darkness, absence of eyes ; but the subject 

 is one on which we are iu darkness and unable to see. No matter what the nature of the physical 

 condition may be, if Dr. Forschammer is correct in allotting distinct physical properties to sis- 

 teen different regions of the ocean, it is not improbable that material differences may exist without 

 our being able to detect them. 



Mr. Darwin relies on other facts characteristic of oceanic islands, more especially of those 

 which have subsided. These facts all fall under the same category, and involve the same principle. 

 They are : — The nature and relative proportion of inliabitants in oceanic islands ; the existence 

 of some families to the exclusion of others (bats to the exclusion of batrachiaus and terrestrial 

 mammals, &c.) ; the scarcity of kinds of animals generally ; and the preponderance of arboreal over 

 herbaceous forms of plants.* 



Now, if we think for a moment of the course of events which must necessarily have taken 

 place on the subsidence of the land of which these islands formed part, there seems nothing in the 

 above facts to justify the idea of colonization, or inconsistent with that of former continuity. The 

 reader will find the probable course of events following upon subsidence speculated on a little more in 

 detail in a subsequent chapter on the Distribution of Man. Here it will be sufficient to say, that as 

 the land became submerged, such animals as existed would for the most part be drowned or starved, 

 unless where they betook themselves to the highest peaks, which remained longest above the waves. 

 If man or carnivorous animals were amongst them, their extinction would only be the more rapid. If 

 none but herbivorous animals took refuge there, the food would be insufficient for numbers, and they 

 would drop off by inanition. It seems also very doubtful whether the peaks which we now see in the 

 centre of the atolls, were in existence when the spot on which they stand was first submerged. They 

 are all of volcanic origin, and may have arisen after the land was drowned. The coral atolls may have 

 originally started from slight elevations on the surface of a flat continent, and man may have been able 

 to maintain his place on these half-dry reefs, which terrestrial animals — excepting always bats and 

 birds — could not. Under such circumstances it is obvious that it would be an inexplicable anomaly 

 were we to find no " scarcity of animals generally." It is equally obvious that all other animals which 

 could neither fly nor swim must be absent. And, as is remarked by Mr. Darwin himself, batrachia 

 must follow in the same category, for they cannot live or propagate in salt water. Therefore their 

 fate would be as much sealed as that of any other class of animals. Mr. Darwin claims the bats as 

 specially supporting his view. He says, " No terrestrial mammal can be transported across a wide 

 space of sea, but bats can fly across." But they at least are the mammals most fitted for preserving 

 their lives so long as any resting-place at all remained. The presence of land-shells on these 

 islands is acknowledged by Mr. Darwin as a special difficulty in his view of the case, as they can 

 neither fly nor swim across a part of the ocean, and neither they nor their eggs can live in salt 



* Darwin, op. cit. p. 427. 



