DEVELOPMENT OF FROG 



675 



to be developed, a direct communication is established 

 between afferent and efferent branchial vessels, so that 

 blood can pass from the heart to the dorsal aorta without 

 going through the gills. As the pulmonary circulation 

 becomes increasingly important, the single auricle of the 

 heart becomes divided into two by a septum, and the pul- 

 monary veins are established. At the time of the meta- 

 morphosis an increasing quantity of blood avoids the gills 

 in the manner indicated above, and these, being thrown out 

 of connection with the rest of the body, soon atrophy, while 

 the lungs become the important respiratory organs. The 

 fate of the various branchial arteries is shown in the 

 following table : 



The tadpole has by this time grown large and strong, 

 feeding in great part on water-weeds. Now it seems to 

 fast, but the tail, which begins to break up internally, 

 furnishes, with the help of phagocytes, some nourishment 

 to other parts of the body. The habit becomes less active, 

 the structural adaptations to the aquatic life disappear. 

 " The horny jaws are thrown off ; the large frilled lips 

 shrink up ; the mouth loses its rounded suctorial form 

 and becomes much wider ; the tongue, previously small, 

 increases considerably in size ; the eyes, which as 



