THE EVIDENCE FOR ORGANIC EVOLUTION 523 



is less impressive than the many special cases presented in the dis- 

 cussion of structure and distribution in the two preceding sections, 

 but at least it corroborates the evidence from other fields. 



Special Physiological Resemblances. — There is, however, one 

 line of physiological evidence that is very specific. It has been 

 ascertained, by methods which need not be here described, that 

 the blood of various animals shows certain ph3\sico-chemical 

 resemblances. Extensive tests have been made, particularly 

 among vertebrates. In general, it is found that animals that are 

 closely related, accord- 

 ing to the classifica- 

 tion based on struc- 

 ture, exhibit a parallel 

 degree of relationship 

 in the physico-chemi- 

 cal nature of their 

 blood. The blood of Yig. 281.— Male (A) and female {B) of the 

 man, for example, is jungle-fowl, Gallus banJdva. 



very mucn like tnat Domestic poultry have apparently all descended from 



of a P'orilla or 1 phini- ^^^ jungle-fowl, now found wild in southern Asia, with 



. sonic admixture from the Aseel or wild Malayan fowl. 



panzee, less like that (After Davenport, Carnegie Institution Pub. 121.) 



of a monkey, and so 



on, showing degrees of relationship that agree closely with the 

 classification of the Mammalia. The blood of any mammal is 

 more like that of other mammals than it is hke the blood of 

 birds or reptiles. Bird blood is like bird blood, reptile hke reptile; 

 but there is a closer resemblance between the blood of birds and 

 that of reptiles than between either one of these and the blood of 

 Mammalia or Amphibia. This is to be correlated with the rela- 

 tionships inferred between birds and reptiles on other grounds 

 (c/. p. 519). The numerous tests that have been made confirm 

 to an amazing extent the degrees of resemblance previously inferred 

 from Anatomy, Embryology, and Paleontology, and expressed in 

 Classification. Thus the chemistry of blood presents remarkable 

 corroborative evidence for the evolutionary theory. 



Observational and Experimental Evidence 



The History of Domestic Animals. — Evidence from observa- 

 tion and experimentation is found in the history of animals and 



