BLOOD AND VITELLINE VESSELS IN AMPHIBIA 365 
As the circulation becomes stronger and as more and more pig- 
ment develops in the embryo and in the blood, the current in all 
the blood vessels on the surface is towards the head, and these 
vessels unite into one which joins the heart (figs. 15 and 16). Just 
at the edge of the body of the embryo the rather large lateral 
cutaneous vein may be seen with its blood flowing towards the 
head end. This may be found in a specimen such as shown in 
figures 17, 26 and 27, at a time when the embryo has begun to 
become twisted on the yolk. The blood on the surface is in the 
splanchnopleure, that in the lateral cutaneous vein is in the soma- 
topleure. The steady stream in the lateral cutaneous vein in 
slightly later stages speaks of an abundant supply and its seems 
quite probable that some of its blood is obtained from the yolk 
surface at an early stage if not in a later one, but no clear indica- 
tion of an anastomosis was found. In later stages the yolk ves- 
sels become more and more prominent, the blood is bright red and 
the flow in the larger vessel more vigorous. 
As the embryo coils more about the yolk, the body-wall or 
somatopleure grows down, and at an early stage, before this has 
been continued very far and before there is much pigment in the 
embryo, a series of vessels on each side enters the lateral cuta- 
neous vein from the edges of the body-wall. There are at first 
about eight of these on a side, more or less equidistant from each 
other. They are parallel and all are perpendicular to the lateral 
cutaneous (figs. 17 and 27). In some specimens their lower ends 
seem at first to be in slight communication with the yolk vessels, 
but as the body-wall continues farther over the yolk these possible 
connections are lost and a line of anastomoses, parallel with the 
cutaneous, connects a number of the ends of the perpendicular 
vessels, so that a more or less closed somatic system (fig. 27) is 
formed. The blood may be seen running under the somatic ves- 
sels and into the larger vitelline, while the blood of the somatic 
parallel may flow either from the cephalic or from the caudal end 
into the perpendiculars. When the first perpendicular somatic 
vessels are developed in connection with the lateral cutaneous they 
do not seem to be connected to each other. ‘There is no circula- 
tion in them and the movement in the lateral cutaneous is slow 
and jerky towards the head end. Later, about the time a parallel 
