THE DEVELOPMENT OF THE BLOOD AND THE TRANS- 
FORMATION OF SOME OF THE EARLY VITELLINE 
VESSELS IN AMPHIBIA . 
WILLIAM A. HILTON 
Department of Histology and Embryology, Cornell University, and the Institute of 
Anatomy, University of Minnesota 
FORTY-FOUR FIGURES 
INTRODUCTION 
While collecting embryonic amphibian material several sum- 
mers ago, I became much interested in the yolk circulation of 
living Desmognathus embryos. In the early stages these animals 
are entirely without pigment and the formation of vascular areas 
shows beautifully on the surface of the pure white yolk. It was 
possible, in the living embryos, to trace the development of the 
blood and blood vessels from the time of their first appearance 
until they were well formed in late larval stages. At first clear 
areas made their appearance on the surface of the yolk mass; 
later these became more extensive and ran together. Still later 
a gradually increasing network of clear lines became evident. 
There were blind ends and disconnected parts in early stages; 
these were afterward seen to form themselves into a closed sys- 
tem which became connected with the heart. As somatic vessels 
were formed in the extensions of the body-wall over the yolk, 
complex changes in the capillaries gave an excellent opportunity 
to observe their methods of growth and their transformations. 
The first observations were made on Desmognathus, but 
other amphibian embryos were studies for comparison. In this 
paper the results from the study of two species of Urodela are 
given. Each of these offered some advantages; Amblystoma, 
with its smaller yolk mass was investigated by means of a large and 
339 
JOURNAL OF MORPHOLOGY, VOL. 24, NO. 3 
SEPTEMBER, 1913 
