194 THE DARWINIAN THEORY 



ence is so close that it is almost impracticable to 

 find any constant points of difference of any value 

 whatever. It has indeed been shown by Professor 

 Huxley that the anatomical differences between 

 man and the higher monkeys are markedly less than 

 those between the higher and lower monkeys. 



Again, as to development, man, like all other 

 animals, commences as a single cell, and passes 

 through a gill-cleft stage indistinguishable from that 

 of other Vertebrates. He has, like other mammals, 

 at one time two aortic arches, a right and a left, but 

 during development he loses the right arch. His 

 brain, eyes, and limbs are all formed in the same 

 manner as in other mammals. 



Rudimentary organs are also present in man, and 

 are of the utmost value, because they are only 

 explicable on the supposition that man is descended 

 from some ancestor in which these organs were in a 

 functional condition. For instance, the intrinsic 

 muscles of the ear are present in man in an in- 

 completely developed form, and in a condition in 

 which they can be of no use to their possessors. So 

 also with the platysma muscle, which, while ex- 

 tensively developed in some Vertebrates, such as 

 horses, is in a comparatively rudimentary condition 

 in man, and of scarcely any functional value. Again, 

 the "wisdom teeth" form another example of 

 rudimentary organs, since they are always cut long 

 after the others, and sometimes never pierce the 

 gums at all. 



The tendency to reversion is also met with in man, 

 and is seen in the more or less complete presence of 



