244 The American Naturalist. [March, 
their base, and the notch between them is diminished; and at the 
end of the third month the ventricles are very little separated from 
one another, though the place where the notch previously existed 
is still strongly marked. 
“In the state of the circulatory system in the early embryo, 
where the heart is as yet but a pulsating enlargement of one of the 
principal trunks, and the walls of the vessels are far from being 
complete, we have the representation of its condition in the higher 
Radiata, and in the lower Articulata and Mollusca. In the sub- 
sequent division of the cardiac cavity into an auricle and ventri- 
cle an advance is made, corresponding to that which we encounter 
in passing from the Truncata to the higher Mollusca. And when 
the branchial arches are formed, which enclose the pharynx and 
meet in the aorta, the type of the fish is obviously attained, and 
at a subsequent period the condition of the heart and great vessels 
presents a strong general resemblance to that of the typical 
reptiles.” 
Even at birth the true mammal heart is still incomplete, for 
there is an opening in the septum between the right and left 
auricles called the foramen ovale, which does not entirely close 
until after birth, and not in all cases then, leaving the child so 
formed in a condition almost certain to lead to early death. 
Does not this opening, which is of no use to fœtus or child, 
seem more likely to be the result of a general evolution, 
gather than of a special creation of a useless and oftentimes a 
harmful accident ? 
There is also, in the fcetal circulation, a connecting vessel be- 
tween the pulmonary artery as it emerges from the right ventricle 
and the aorta as it leaves the left ventricle. This ductus arteri- 
osus soon becomes obliterated after birth, so that man has only 
temporarily what is persistent through life in the reptile. 
The peculiar relation of the valves of the veins to the vessels 
they occupy in man has furnished Dr. S. V. Clevenger, of Chicago, 
the material for a striking argument for the evolutionary origin 
of man. (See American Naturatist, Vol. XVIII.) 
The veins which return the blood to the heart against gravity, 
as in the legs and arms, are supplied with valves which allow the 
