DEVELOPMENT OF FisH EmBryos 297 
a circulation of the blood in the vessels. In syite of this 
fact, a complete circulatory system was developed which did 
not differ markedly, in regard to the direction and the 
branching of the vessels in the embryo and in the yolk-sac, 
from that of a Fundulus embryo developed in normal sea- 
water. Heaps of red-blood corpuscles were found in the large 
blood-vessels, such as the arteries of the yolk at the point 
where they leave the embryo. 
The important result of these observations is therefore 
the fact that « complete vascular system, which is probably 
identical in its main distribution and in its two vascular 
divisions with that found in the normal embryo, can be 
formed without a circulation, and therefore without blood- 
pressure. A difference between the two, which also deter- 
mines the limit of the possible identity of the vascular sys- 
tems in the normal and abnormal embryos, is found in this, 
that the lumina of the vessels in the poisoned embryo are 
exceedingly irregular. The lumen of a vessel is in extreme 
cases rosary-like, narrow and wide spots alternating with 
each other. This is due to the absence of a sufficient intra- 
vascular pressure. 
3. It might have been possible that a circulation lasting 
only a short time had been present which I did not dis- 
cover. I therefore made experiments with much stronger 
KCl solutions—such in which not even a trace of cardiac 
activity ever appeared. In extreme cases I addded 5 g. of 
KCl to 100 c.c. of sea-water. J had previously ascertained 
that a four-day-old embryo which had developed in normal 
sea-water dies in two minutes in a 3 per cent. KCl solution. 
Nevertheless, the fertilized eggs developed normally in a 5 
per cent. KCl solution. They developed for three to six 
days, and formed—what is of interest to us here—a heart 
and a typical vascular system in the embryo and yolk-sac. 
On the other hand, the development of the embryo as a 
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