TERTIARY CIRCULATORY SYSTEM. 4OI 



show that the germ-history of Man (according to the law 

 of abbreviated heredity) is very rapid and compressed in 

 the first stages of its course, but grows slower and slower 

 in each succeeding stage. All the remarkable phenomena 

 which we observe in the transformation of the human 

 embryo in the whole course of our Ontogeny, are intel- 

 ligible only with the help of Phylogeny, and are explicable 

 only by reference to the historical metamorphoses of our 

 animal ancestry.^^^ 



It is true that if the ontogenetic, and the phylogenetic 

 stages (in Tables VIII. and XXII.) are carefully compared, 

 a complete agreement between the two is not observable ; 

 on the contrary, there are many individual divergences. In 

 germ-history many organs ajDpear earlier, others latei', 

 than the probable course of tribal history leads us to 

 expect. But an adequate explanation of these divergences 

 is found in the various kenogenetic modifications which 

 the germ-history of the higher Vertebrates has undergone 

 in the long course of its evolution. This will become quite 

 clear when we carefully compare the germ-history of Man 

 with the Ontogeny of the lowest Vertebrate, the Amphioxus, 

 an Ontogeny distinguished by tenacious inheritance of the 

 original course of evolution. 



