1892.] Embryology. 527 



sides, to connect with certain vessels in the trunk. Thus each limh 

 contains a venous loop forming a border along the free tip of the 

 limb, the foot. 



As the digits form, the border vein becomes interrupted, but radial 

 vessels remain between the digits. Various changes take place in the 

 limbs of the venous loop, one limb soon disappearing so that but one of 

 the original two connections between foot and trunk remains. 



Later changes become too complex to be easily expressed in small 

 compass and may be here passed over. Most of the work was done 

 upon living specimens, so that the direction of blood-flow and certain 

 interesting changes from artery to vein function could be observed. 



In the Anamnia the author found in a Triton that though there 

 is no border vein yet there is a vascular loop for each limb and later, 

 when the digits appear successively, there is a duplication of this loop 

 for each digit, producing a resulting arrangement not utterly different 

 from the later stages of the border vein in the Amniota. 



Endothelium and Blood Corpuscles in the Amphibia. 1 — 

 Dr. Shwink has made a detailed study of the formation of the endo- 

 thelial lining of the heart and chief vessels and of the origin of the 

 blood corpuscles in the Am m Bui <j Is and liana fusca as well 

 as in the urodeles Triton alpestris and Salamandra atra. In these 

 amphibians the author finds evidence that the cells forming the blood 

 vessels arise, in part at least, in the entoblast and not in the mesoblast. 

 Though he cannot exclude the mesoblast entirely, yet he fails to find 

 evidence that it has any part to play in forming the endothelium, and 

 regards the yolk-entoblast as forming most, if not all, of the endothe- 

 lium cells. 



The blood corpuscles arise later than the endothelial cells. They 

 are made in three blood-islands posterior to the heart into which they 

 are then carried by the movement of the serum. The nuclei of the 

 corpuscles do not come from yolk spherules but from pre-existing 

 nuclei which divide actively in the first formed corpuscles. 



In the Anura the blood corpuscles are not formed from the meso- 

 blast but from the yolk-entoblast. Yet this may be a recent departure 

 from a phylogenetically older formation of blood cells from some 

 mesoblast that is now incorporated in the entoblast. In the urodeles 

 the evidence is conflicting and at present the author is unable to 

 to decide whether the blood-islands are of mesoblastic or of entoblastic 

 origin or in part of both. 



Worph. Jahrb., 7, 1891, pp. 288-331 , plates 17-19. 



