PHYLOGENY 261 



of the facts which have been arrayed as a proof or demonstration 

 of vertebrate origin from the invertebrates. 



Similarity in structure and development and even homologies 

 between the members of two animal groups do not prove that 

 one has originated from the other. At most, they point to a 

 common heritage. Our various theories demonstrate undis- 

 puted interrelationships between the chordate phylum and the 

 non-chordates, but the key to the ancestry of the vertebrates 

 lies hidden, possibly lost, in some form of past ages which has 

 been an ancestor alike to the vertebrates and the higher inverte- 

 brates and through which both of these groups have inherited 

 the characters which they hold in common. A search for this 

 ancestral form among the highly differentiated animal forms of 

 today is little short of hopeless. 



References 



Delsman, H. C. 1922. "The Ancestry of Vertebrates as a Means of 

 Understanding the Principle Features of Their Structure and Develop- 

 ment." Weltevreden (Java). 



Gaskell, W. H. 1908: "The Origin of the Vertebrates." London, Long- 

 mans Green. 



HuBRECHT, A. A. W. 1883: On the Ancestral Form of the Chordata. 

 Quart. Jour. Micr. Sci., N. S., 23: 349-368. 



Lull, R. S. 1917: "Organic Evolution." New York, Macmillan. 



MacBride, E. W. 1914. "Text-book of Embryology." Vol. 1, "Inverte- 

 brata." London, Macmillan. 



OsBORN, H. F. 1917. "The Origin and Evolution of Life." New York, 

 Scribners. 



Patten, W. 1912. "The Evolution of the Vertebrates and Their Kin." 

 Philadelphia, Blakiston. 



Semper, C. 1875. Die Stammesverwandtschaft der Wirbelthiere und 

 Wirbellosen. Arbeit. Zool. Zoot. Inst. Wurzburg, 2: 25-76. 



Walcott, C. D. 1899: Pre-Cambrian Fossiliferous Formations. Bull. 

 Geol. Soc. Amer., Apr. 6, 1899: 199-244. 



Wilder, H. H. 1909. "History of the Human Body." New York, Holt. 



