354 THE EVOLUTION OF MAN. 



claims to have caused by his new conception of genrv 

 history, is, according to him, his discovery that " the blood 

 and tissue of the connective substance" (that is to say, the 

 greatest part of the vascular system) " do not originate from 

 the two primary germ-layers, as do all the other organs, 

 but from the elements of the white yelk." The latter 

 is designated as " supplementary yelk, or parablast," to 

 distinguish it from the "main-germ, or archiblast" (the 

 germ-disc composed of the two primary germ -layers). 



The whole of this artificial development theory of His, 

 and above all the unnatural distinction between the supple- 

 mentary and the main germ, collapses like a card house 

 when the Anatomy and Ontogeny of the Amphioxus, that 

 invaluable lowest Vertebrate, is contemplated, which alone 

 can elucidate the most difficult and darkest features in the 

 development of the higher Vertebrates, and thus also of 

 Man. The gastrula of the Amphioxus alone overthrows 

 the whole artificial theory ; for this gastrula teaches us 

 that all the various organs and tissues of complete Verte- 

 brates originally developed entirely from the two primary 

 germ-layers. The developed Amphioxus, like all other 

 Vertebrates, has a differentiated vascular system and 

 a skeleton of "connective substance tissues" extending 

 throughout its body, and yet there is in this case no "sup- 

 plementary germ " from which these tissues can originate 

 thus, contrasting with the other tissues. 



The larva; of the Amphioxus, arising from the original 

 bell-gastrula (archigastrula), in its further development, 

 throws the most important rays of light also upon the diffi- 

 cult history of development of the vascular system. In the 

 first place, it answers the very important question, which 



