FREE BOOKS

Author's List




PREV.   NEXT  
|<   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80  
81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   103   104   105   >>   >|  
, Ed. i. p. 438, vi. p. 602, the author, referring to the expressions used by naturalists in regard to morphology and metamorphosis, says "On my view these terms may be used literally." <_Embryology._> This general unity of type in great groups of organisms (including of course these morphological cases) displays itself in a most striking manner in the stages through which the foetus passes{156}. In early stage, the wing of bat, hoof, hand, paddle are not to be distinguished. At a still earlier <stage> there is no difference between fish, bird, &c. &c. and mammal. It is not that they cannot be distinguished, but the arteries{157} <illegible>. It is not true that one passes through the form of a lower group, though no doubt fish more nearly related to foetal state{158}. {156} See _Origin_, Ed. i. p. 439, vi. p. 605. {157} In the _Origin_, Ed. i. p. 440, vi. p. 606, the author argues that the "loop-like course of the arteries" in the vertebrate embryo has no direct relation to the conditions of existence. {158} The following passages are written across the page:--"They pass through the same phases, but some, generally called the higher groups, are further metamorphosed. ? Degradation and complication? no tendency to perfection. ? Justly argued against Lamarck?" This similarity at the earliest stage is remarkably shown in the course of the arteries which become greatly altered, as foetus advances in life and assumes the widely different course and number which characterize full-grown fish and mammals. How wonderful that in egg, in water or air, or in womb of mother, artery{159} should run in same course. {159} An almost identical passage occurs in the _Origin_, Ed. i. p. 440, vi. p. 606. Light can be thrown on this by our theory. The structure of each organism is chiefly adapted to the sustension of its life, when full-grown, when it has to feed itself and propagate{160}. The structure of a kitten is quite in secondary degree adapted to its habits, whilst fed by its mother's milk and prey. Hence variation in the structure of the full-grown species will _chiefly_ determine the preservation of a species now become ill-suited to its habitat, or rather with a better place opened to it in the economy of Nature. It would not matter to the full-grown cat whether in its young state it was more or less eminently feline, so that it become so whe
PREV.   NEXT  
|<   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80  
81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   103   104   105   >>   >|  



Top keywords:

Origin

 

structure

 

arteries

 
chiefly
 

distinguished

 

author

 

mother

 
adapted
 

foetus

 

passes


species

 

groups

 
suited
 

artery

 

passage

 
occurs
 

preservation

 

identical

 

wonderful

 

habitat


advances
 

altered

 
greatly
 

remarkably

 

feline

 

assumes

 

widely

 

eminently

 
mammals
 

characterize


number
 

determine

 

economy

 

matter

 
opened
 

propagate

 

degree

 

whilst

 
Nature
 

secondary


earliest

 

kitten

 

thrown

 

theory

 
sustension
 

variation

 

organism

 

habits

 
stages
 

displays