ABSTRACT
The lungs of tadpoles of R. temporaria were removed at an early stage (12 mm.) in order to ascertain the effect on the development of the atrium and the interauricular septum of the heart. Serial sections of the hearts of experimental and control tadpoles at three comparable stages of development between the operation and metamorphosis were prepared.
The operation causes a reduction in the absolute volume of the atrium.
When it is first formed, the left auricle in the normal tadpole averages 25 per cent, of the total atrial volume but, as growth proceeds, it comes to average about one-third of the total atrial volume by the time metamorphosis occurs. In the experimental tadpoles the left auricle, when first formed, averaged about one-fifth of the total atrial volume and maintained a similar proportion throughout development to metamorphosis. The presence of the pulmonary return is thus necessary for the normal enlargement of the proportional volume of the left auricle.
The obliteration of the pulmonary return did not affect the origin and normal development of the interauricular septum.