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I II III IV V 



Stages in the metamorphosis of Rana pipiens. (Stage I) The oral sucker elevations 

 have completely disappeared. Four rows of labial teeth are present, one pre-oral and 

 three post-oral. Chromatophores have appeared and become numerous on the dorsal 

 and lateral surfaces, and extend progressively ventrad. The limb bud is visible as a 

 faintly circumscribed elevation in the groove between the base of the tail and the belly 

 wall. The height of the elevation is less than half the diameter of the disk. {Stage H) 

 The height of the limb bud elevation (i.e., the length of the bud) is equal to half of 

 its diameter. The first row of post-oral labial teeth is usually at the middle to form a 

 pair of crescents. On the dorsal surface of the head the lateral line system is becoming 

 conspicuous as pigment-free lines, especially in darkly pigmented individuals. The 

 melanophore patches covering the gill region on either side usually meet in a narrow 

 band ventral to the heart. (Stage 111) The length of the limb bud is equal to its 

 diameter, and it continues to grow both in length and diameter at an approximately 

 equal rate. This stage is relatively long in duration. (Stage IV) The length of the limb 

 bud is equal to one and a half times its diameter. (Stage V) The length of the limb 

 bud is twice its diameter. The distal half of the bud is bent ventrad. There is no flatten- 

 ing of the tip. (Continued on facing page.) 



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