342 WILLIAM A. HILTON 
evidence of it. The development of blood vessel endothelium 
from isolated cells as described by Mollier (’06), Greil (08) and 
others, seems to be somewhat different from the growth of lym- 
phatie vessels from sprouts as described by Clark (’09), in the 
tail of a frog tadpole. The development of blood vessels from 
capillary networks as described by Evans (’09) in certain verte- 
brate embryos, may not seem, at first sight, to be in accord with 
other work on Amphibia; but this lack of agreement may be ex- 
plained by supposing that the early circulation was a'most of an 
invertebrate type, merely in spaces before the capillary walls 
were developed, and that later certain of these channels were 
selected for the main blood vessels and gradually developed a 
more complete endothelium. 
REVIEW OF LITERATURE RELATING TO THE EARLY ORIGIN OF THE 
BLOOD AND VASCULAR SYSTEM OF AMPHIBIA 
Reichert (40) believed that the heart in Amphibia developed 
from part of the original head yolk-mass and was at first solid. 
Remak (’50) made similar observations on the development of 
the heart and he probably recognized the fold cavity into which 
it develops. Van Bambeke (’67) considered the heart to come 
from the visceral layer of the mesoderm in Pelobates. Oellacher 
(71) believed that the heart endothelium came from a fold from 
the splanchnic mesoderm, a line of cells being formed which folded 
off into a delicate tube. 
Goette (’75) thought that the endothelium of the heart of Bom- 
binator igenus came from a loose cell group detached from the 
ventral wall of the fore-gut. The blood vessels, to some extent, 
develop independently of the heart and blood, as spaces in meso- 
dermic connective tissue, the walls being formed by cells migrat- 
ing from the early yolk-formed blood masses. The corpuscles, 
according to him, arose from an unpaired blood island which 
forked in front at the level of the liver. Some of the vascular 
endothelium arises from this area, which also furnishes blood 
corpuscles. 
Rabl (’87) describes the heart in Amphibia as arising between 
the mouth and liver and probably coming from entoderm. In 
