SELECTION 



movement when the bird is in the water, while the 

 long wings of the albatross are held motionless 

 during the greater part of the day. Here natural 

 selection has over-ridden use-inheritance. Or 

 compare the cartilaginous skeleton of the rapidly 

 swimming shark with the bony skeleton of the slug- 

 gish eel. In this case also it is difficult to think 

 that use-inheritance has been the cause of the better 

 development in the eel. 



It is, as I have just said, in the various contri- 

 vances for bringing about the same end that we 

 recognise the action of natural selection most 

 readily. For example, the means adopted by the 

 land-snails for breathing air are different in the two 

 groups. In the Pulmonifera the lung, which is 

 lined with blood-vessels, is a cavity formed by a 

 folding of the mantle on the right side. While in 

 the Cyclostomatidae it is a reticulated organ, situated 

 in a cavity in the body on the back of the neck, and 

 in front of the mantle. So also in the land-crabs 

 the orifice for the air is formed in a different manner 

 in each of the families. One more illustration will 

 suffice. No two birds exhibit a greater contrast than 

 a penguin and an albatross. The one incapable of 

 flight , but the most expert diver among birds ; the 

 other incapable of diving, but the queen of flyers. 

 And yet anatomists tell us that the penguins have 

 their nearest relatives in the petrels. These two 

 different forms, each so thoroughly adapted for get- 

 ting its living on the ocean, have been produced 

 from the same parent stock by the action of natural 

 selection. 



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