4O GENERAL PRINCIPLES OF ZOOLOGY. 



from the single-toed horse of the present day to the four- 

 toed EoJiippos of the Eocene ; for all the hoofed animals a 

 common starting-point or ancestral form has been found in 

 the Condlylarthra. Farther transitional forms have been 

 found between the greater divisions, as, e.g., between 

 reptiles and birds, the remarkable toothed birds, and the 

 ArcJiceopteryx (Fig. 2), a bird with along, feathered, lizard- 

 like tail. 



F:G. 2. Archteopttryx lithographica. (After Zittel.") cl, clavicle; co, coracoid ; h, 

 humerus ; r, radius ; a, ulna ; c, carpus ; I-IV, digits ; sc, scapula. 



(3) Morphological Proofs. If we wish to employ 

 Comparative Anatomy and Embryology in support of the 

 Descent Theory, we find that the two studies have so many 



