82 CHARLES E. STOCK ARD 



nective tissue. If the aorta did arise from this group of cells 

 its cavity is scarcely of an origin comparable to that of the coelom. 

 Its endothelial wall is certainly much the same as that of the 

 lymph vessels. 



The cavities of the nephric duct, ovarian duct, kidney tubules 

 and other tubules derived from the mesoderm are not usually 

 considered to be parts of the coelomic cavity. The blood and 

 lymph vessels do arise from the mesoderm but not in such a way 

 that their cavity can be readily homologized with the coelomic 

 space originating between the lamellae of the mesoderm. The 

 vessels on the yolk-sac of the Teleosts are formed from discon- 

 nected wandering mesenchyme cells which are easily demon- 

 strated. The cavity of these vessels surely cannot be interpreted 

 to arise between mesenchyme cells some of which are derived 

 from the somatic and some from the splanchnic mesodermal 

 layers. The yolk vessels in Teleosts arise by arrangement of 

 mesenchyme cells and so apparently do other vessels within 

 the embryo. Thus these blood vessels are similar in origin 

 to the lymphatics according to Felix's notion of the mesenchymal 

 origin of lymphatics. The numerous recent investigators of 

 the origin of the lymphatics, athough to some extent divided 

 into two schools, all treat the lymph vessels and blood vessels 

 as being of the same general genetic type Sabin ('13) and Hunt- 

 ington ('14). 



Finally, the most" damaging evidence against Felix's notion 

 that the blood vascular spaces are derived from the coelom, 

 and that these spaces are actually now comparable to the coelo- 

 mic space is the following: Before a true coelom, such as that 

 to which Felix refers in the vertebrates, has arisen in the animal 

 series blood vessels are already present and these vessels often 

 communicate with or are actually a part of the primary body 

 cavity. When the true coelom does arise in the invertebrate 

 series blood vessels never open into its cavity or communicate 

 with it. Felix has therefore derived an older and more general- 

 ized animal system from a newer or later formation. This 

 of course is contrary to any principle of phylogenetic calcula- 

 tions. 



