DESCENT OF MAN FROM SOME LOWER FORM. 139 



use, the power of largely moving their scalps up and 

 down. 



p It is well known that in the males of all 



mammals, including man, rudimentary mam- 

 mae exist. These in several instances have become well 

 developed, and have yielded a copious supply of milk. 

 Their essential identity in the two sexes is likewise shown 

 by their occasional sympathetic enlargement in both dur- 

 ing an attack of the measles. 



"NO OTHER EXPLANATION HAS EVER BEEN GIVEN." 



r, -i The homological construction of the whole 



Page 24. ° 



frame in the members of the same class is 

 intelligible, if we admit their descent from a common 

 progenitor, together with their subsequent adaptation to 

 diversified conditions. On any other view, the similarity 

 of pattern between the hand of a man or monkey, the 

 foot of a horse, the flipper of a seal, the wing of a bat, 

 etc., is utterly inexplicable. It is no scientific explana- 

 tion to assert that they have all been formed on the same 

 ideal plan. With respect to development, we can clearly 

 understand, on the principle of variations supervening at 

 a rather late embryonic period, and being inherited at a 

 corresponding period, how it is that the embryos of won- 

 derfully different forms should still retain, more or less 

 perfectly, the structure of their common progenitor. Ko 

 other explanation has ever been given of the marvelous 

 fact that the embryos of a man, dog, seal, bat, reptile, 

 etc., can at first hardly be distinguished from each other. 

 In order to understand the existence of rudimentary 

 organs, we have only to suppose that a former progenitor 

 possessed the parts in question in a perfect state, and that 



