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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- 

 caval openings must be vastly different from what they are in the mammal 

 — but 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 cumulation 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 septum 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 



