300 CHARLES R. STOCK ARD 



3. Vascular endothelium, and vascular growth and development 



Mollier ('06) concludes in his review regarding the origin of 

 vessels as follows. 



As to the genesis of embryonal vessels we may pass the judgment 

 that the theor}^ of the local origin of the vascular endothelium is val- 

 uable. The notion of His ('75) and Vialleton ('92) that the vessel 

 strands of the embryo grow in as sprouts from the extra-embryonal 

 anlage (vascular anlage) is not nearly so probable as that the individual 

 vessel cells arise in loco and thus form the vascular nets. 



This statement agrees in every way with the contentions 

 so fully presented by Huntington ('10, '14), McClure ('10, '12) 

 and others, regarding the origin of lymph vessels. Lately it 

 receives additional substantiation from the experimental results 

 recorded by Miller and McWhorter ('14) on the origin of blood 

 vessels in the chick embryo. Such a position is further strength- 

 ened by the still more recent experimental evidence, presented 

 by Reagan ('15) which shows the origin in loco of vessels in 

 isolated parts of chick embryos. All of these experiments con- 

 firm the earlier results of Hahn ('09) on the origin of vessels in 

 the chick. 



In the Teleost embryos studied during the present investi- 

 gation there can be no doubt that the heart endothelium and 

 aortae arise in loco within the embryo, and here there are no 

 vessels, or even mesoderm, present on the yolk-sac in the an- 

 terior portion. Certain vessels do partially grow from the em- 

 bryo out on to the yolk-sac and other smaller vessels arise in 

 many separate regions of the yolk-sac as the products of wan- 

 dering mesenchyme cells which become arranged to form the 

 tubular vessels. All of these vessels after they have arisen may 

 grow by budding or sprouting off new vessels or may increase 

 in length by a forward growth so well described in living embryos 

 by E. R. Clark ('09, '12) in his careful studies of this subject. 



Felix ('97) describes the origin of the aorta as follows: 



The 'mesenchymaortenstrang' arises from the two lines of sclerotoms 

 after they are finally pinched away from the somites. No fusion of 

 cell material occurs between this and the 'venenstrang/ the inter- 

 mediate cell mass. This 'mesenchymaortenstrang' comes from that 



