HIS ON THE VASCULAR SYSTEM. 351 



erroneous views. By many influential embryonic adap- 

 tations, among which the development of an extensive 

 nutritive yelk must be regarded as the most important, the 

 original course of development of the vascular system ha 

 been so altered, vitiated, and abbreviated, in the higher 

 Vertebrates, that no, or very little, trace of many of the 

 most important phylogenetic features are retained in the 

 Ontogeny. Such explanation as is afforded by the latter 

 would be entirely useless to us if Comparative Anatomy 

 did not lend its aid, and afford us the clearest guidance in 

 our search for tribal history. 



Comparative Anatomy is, therefore, especially important 

 in helping us to understand the vascular system, and, 

 equally, the skeleton system, so that, without its guidance, 

 it is unsafe to take a single step in this difficult field. 

 Positive proof of this assertion can be gained by studying 

 the complex vascular system as explained in the classical 

 works of Johannes Miiller, Heinrich Rathke, and Karl 

 Gegenbaur. An equally strong negative proof of the asser- 

 tion is afforded by the ontogenetic works of Wilhelm His, 

 an embryologist of Leipsic, who has no conception of Com- 

 parative Anatomy, nor consequently, of Phylogeny. In 

 1868, this industrious but uncritical worker published cer- 

 tain comprehensive " Studies of the First Rudiment of the 

 Vertebrate Body," which are among the most wonderful 

 pi eductions in the entire literature of Ontogeny. As the 

 author hopes to attain a " mechanical " theory of develop- 

 ment by means of a most minute description of the germ- 

 history of the Chick alone, without the slightest reference 

 to Comparative Anatomy and Phylogeny, he falls into 

 errors which are unparalleled in the whole literature of 



