Morphology. 65 



of a mollusk. In other words, its peculiar structure 

 is not specially in keeping with its present habits, 

 although so curiously allied to the similar structure 

 of certain other crabs of totally different habits, in 

 relation to which the peculiarities are of plain and 

 obvious significance. 



I will devote the remainder of this chapter to 

 considering another branch of the argument from 

 morphology, to which the case of Birgus serves as 

 a suitable introduction : I mean the argument from 

 rudimentary structures. 



Throughout both the animal and vegetable king- 

 doms we constantly meet with dwarfed and useless 

 representatives of organs, which in other and allied 

 kinds of animals and plants are of large size and 

 functional utility. Thus, for instance, the unborn 

 whale has rudimentary teeth, which are never des- 

 tined to cut the gums ; and throughout its life this 

 animal retains, in a similarly rudimentary condition, 

 a number of organs which never could have been of use 

 to any kind of creature save a terrestrial quadruped. 

 The whole anatomy of its internal ear, for example, 

 has reference to hearing in air or, as Hunter long ago 

 remarked, " is constructed upon the same principle as 

 in the quadruped '' ; yet, as Owen says, " the outer 

 opening and passage leading therefrom to the tym- 

 panum can rarely be affected by sonorous vibrations 

 of the atmosphere, and indeed they are reduced, or 

 have degenerated, to a degree which makes it difficult 

 to conceive how such vibrations can be propagated to 

 the ear-drum during the brief moments in which the 

 opening may be raised above the water." 



* F 



