lO THE DOCTRINE OF DESCENT, 



four toes. Earlier writers were content to say that the 

 astragalus (c) replaces the tarsus and metatarsus. But 

 this is not the case; for the chick in the egg (B) shows 

 that the bird's leg consists of the thigh, or femur (o), and 

 the shank or tibia (b), two tarsal (m, n), and three or four 

 metatarsal bones (c), and the toes, or phalanges; that 

 the upper tarsal bone is anchylosed with the tibia, and 

 the lower one with the consolidated metatarsus. Only 

 thus do we obtain a true perception of the fact manifested 

 in A, although the cause of the fact does not as yet ap- 

 pear. 



The next example is rather more difficult. With- 

 out the history of development, comparative anatomy is 

 incapable of explaining why man possesses three little 

 bones in the auditory apparatus, the bird only one. The 

 history of development shows that out of the material 

 which in man is applied to the formation of the malleus 

 and incus, two other portions of the skull are evolved in 

 the bird, having little or nothing to do with the auditory 

 mechanism. In short, the history of development, which 

 describes the gradual formation of the organism, is at 

 every step a beacon to comparative anatomy. In itself, 

 however, the history of development does riot as yet 

 exceed the rank of a merely descriptive branch of erudi- 

 tion. 



But if we now perceive how the evolutionary stages 

 of individuals represent series from the lower to the 

 higher, analogous to the various members existing side 

 by side in the same group of animals, — how, for instance, 

 the mammal passes through stages at which the lower 

 vertebrata remain fixed, — a connection, at first sight 

 mysterious, is indicated between the evolution of the 



