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note that the higher mammals carry the offspring to term; the marsupials 
have a short period of gestation, and while the young are born in a very 
immature condition, they are brooded in a sac (marsupium) ; the mono- 
treme’s method does not differ essentially from that of the bird save per- 
haps in the mode of the incubation of the egg and the postembryonal care 
of the offspring. It would therefore be a logical inference to grant that 
the circulatory conditions in the fetal mammal and bird were about the 
same. Indeed the von Haller-Sabatier theory has been carried over di- 
rectly to the bird, i. e., the right heart of the fetal bird is described as 
venous, the left as arterial. 
I have stated that the latest text-book on chick embryology translates 
this blood segregation theory from mammal to bird with no comment on 
its defects. If the postcaval vein in the chick does carry the arterial 
blood richly laden with nourishment from the yolk to the left auricle 
through the foramen ovale, then the relations of the precaval to the post- 
‘aval openings must be vastly different from what they are in the mammal 
—pbut they are not. Further, if this is a developmental necessity, what 
is the character of the circulation in the anomalies where the right precaval 
opens with or into the postcaval? Is it possible for the described condi- 
tions to obtain in these cases or in Rhea’ americana, where, according to 
Gasch (2), the common opening of the right precaval and the post caval is the 
normal. I have no experimental evidence to bring up as yet for the mixing 
of the blood in the right auricle of the bird, but I believe there is sufficient 
ground for the claim that it occurs from the similarity to the mammal 
in heart structure, developmental requirements, and from the aberrant 
types such as I have mentioned. 
Phylogenetically the connecting link between bird and reptile is par- 
ticularly strong; ontogenetically the requirements for development differ 
only in body temperature (viviparous forms excluded), and we would 
therefore expect little difference in the character of blood circulation, al- 
though the heart structure is quite different. Taking the turtle as the 
type, the described circulation is about as follows: the right auricle is 
venous, the left auricle arterial—both open into the incompletely divided 
ventricle by separate openings. The blood from these two sources is 
segregated in corresponding parts of the ventricle, and when the ventricle 
contracts, the incomplete septuni touches the ventricular wall, isolating a 
part of the venous blood in a sort of right chamber of the ventricle. The 
venous blood is expelled through the pulmonary artery, mixed blood is 
