CHAPTER VII. 



THE DISTEIBUTIOlSr OF ANIMAL LIFE. 



In order to appreciate the force of the Darwinian 

 theories, a clear appreciation of the effect of geogra- 

 phical conditions upon animal life is very necessary. 

 The effect of the present distribution of land and sea 

 is easily understood. Terrestrial animals cannot pass 

 a wide stretch of ocean, nor aquatic animals pass a 

 barrier of land ; and isolated lands or isolated seas are 

 therefore apt to present peculiar types. These types 

 are often archaic, or old-fashioned; that is to say,they 

 present features which, on the Darwinian hypothesis, 

 we should suppose to mark them as oldei- kinds, be- 

 longing to a past age, and resembling those of extinct 

 animals represented now only by remains existing in 

 geological strata. These types are not so highly 

 specialized; that is to say, some of their organs present 

 a form which we may easily suppose to be the begin- 

 ning of those organs as they exist in other and more 

 familiar types, but without all the latest improve- 

 ments which these other and more familiar types 

 possess. The archaic types of animal, in short, 

 present in their build the same relationship to the 

 more widely distributed types that the first locomo- 

 tive or the first sewing-machine presents to those 



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