The Development of the Frog 63 



through that passage than to pass through the 

 fine capillaries of the gills, so that the supply 

 of blood to the gills is gradually cut off, and 

 the amount of blood that goes to the lungs is 

 correspondingly increased ; but for a time the 

 tadpole breathes both by gills and by lungs. 



If the tadpole be prevented from coming to 

 the surface to breathe, as by fastening wire 

 netting just below the surface of the water, it 

 is said that the change to the lung-breathing 

 condition may be indefinitely postponed. 



The changes in the circulation that take 

 place at metamorphosis are chiefly concerned 

 with changes in the branchial blood vessels, 

 or, as they are called after the disappearance 

 of the capillaries and the establishment of 

 the direct communication, the aortic arches. 

 Some of the details of these changes have not 

 been made out as satisfactorily as is to be de- 

 sired, but the main points are pretty definitely 

 established. 



Since the branchial blood vessels in the man- 

 dibular and hyoid arches are, from the first, 

 rudimentary, they may be disregarded in this 

 discussion. After the establishment of the di- 

 rect communication between the afferent and 

 efferent branchial vessels, the blood passes 



