288 FROGS, TOADS, AND NEWTS [CH. VIII 



In this stage the tadpole feeds voraciously and attains 

 a length of over an inch, and now that its powers of 

 swimming are considerable its adhesive mucous organ is 

 of less importance and dwindles away. 



At about the sixth or seventh week the hind limbs 

 begin to appear as a pair of small warts at the base of 

 the tail ; these steadily lengthen, become jointed and, at 

 about the eighth or ninth week, develop toes. The front 

 limbs are not visible till somewhat later. They arise at 

 about the same time, but are concealed beneath the 

 operculum. They eventually become free from the cover- 

 ing, the right leg forcing its way through, and the left by 

 pushing out at the spout. 



In about the eleventh or twelfth week a profound 

 change takes place in the entire economy of the tadpole. 

 It ceases feeding; the outer layer of the skin is cast off; 

 the eyes come to the surface; the horny jaws are lost 

 and the fringing lips shrivel ; the mouth and tongue 

 increase in size; the gills are gradually absorbed and 

 their function taken on by the lungs, the gill-slits closing 

 up; corresponding changes also take place in the blood 

 vessels and the pulmonary circulation is established. For 

 a time both lungs and gills are functional concurrently; 

 tadpoles that still possess gills may often be seen to rise 

 to the surface and take air directly, rolling over so as 

 to bring the ventral surface of the body uppermost as 

 they do so. The character of the food is also changed, 

 henceforth the animal is entirely carnivorous. The diges- 

 tive organs undergo alteration related to this change of 

 habit; the stomach enlarges to receive the more bulky 



