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CHRONOLOGICAL SUMMARY OF ORGAN ANLAGEN 



15 mm. total body length stage: 



Notochordal cartilage sheath develops, vertebrae begin to appear, 

 saccule gives rise to lagena (cochlea) and to a basilar chamber, sen- 

 sory patches appear in ear epithelium, lateral line organ fully devel 

 oped, mesonephric tubules associated with median cardinal vein. 



Metamorphosis at 75 to 90 days: 



Loss of horny jaws, widening of mouth, shortening of gut and 

 changing of its histology to conform with a change from vegetable 

 diet to an omnivorous diet, loss of tail with its 32 pairs of spinal 

 nerves and development of two pairs of legs, shedding of larval skin, 

 disappearance of lateral line system as frog leaves aquatic environ- 

 ment, loss of caudal veins, full development of tongue, active func- 

 tioning of endocrine glands (particularly thyroid and pituitary), and 

 appearance of differentiated gonads containing maturing gametes. 



The finished product of normal frog embryology. (Copyright by General 

 Biological Supply House, Chicago.) 



