372 GENERAL SUMMARY [Part II. 



from the nature of the organism and the action of the sur- 

 rounding conditions, or from changed habits of life, no 

 single pair will have been modified in a much greater de- 

 gree than the other j)airs which inhabit the same country > 

 for all will have been continually bleflded through free 

 intercrossing;. 



By considering the embryological structure of man — 

 the homologies which he presents with the lower animals 

 ■ — the rudiments which he retains — and the reversions to 

 which he is liable, we can partly recall in imagination the 

 former condition of our early progenitors ; and can ap- 

 proximately place them in their proper position in the 

 zoological series. We thus learn that man is descended 

 from a hairy quadruped, furnished with a tail and pointed 

 ears, probably aboreal in its habits, and an inhabitant of 

 the Old World. This creature, if its whole structure had 

 been examined by a naturalist, would have been classed 

 among the Quadrumana, as surely as would the common 

 and still more ancient progenitor of the Old and New 

 World monkeys. The Quadrumana and all the higher 

 mammals are probably derived from an ancient marsupial 

 animal, and this through a long line of diversified forms, 

 either from some reptile-like or some amphibian-like crea- 

 ture, and this again from some fish-like animal. In the 

 dim obscurity of the past we can see that the early pro- 

 genitor of all the Vertebrata must have been an aquatic 

 animal, provided with branchiae, with the t>vo sexes united 

 in the same individual, and with the most important 

 organs of the body (such as the brain and heart) imper- 

 fectly developed. This animal seems to have been more 

 like the larvae of our existing marine Ascidians than any 

 other known form. 



The greatest difficulty which presents itself, when we 

 are driven to the above conclusion on the origin of man, 



