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THE ENDODERMAL DERIVATIVES 



Thyroid gland at the time of metamorphosis. {Top, left) A portion of a 

 follicle at the tail resorption stage. Note the considerable number of para- 

 follicular cells. The cells adjoining the colloid show the highly elaborated Golgi 

 network. {Top, right) A follicle of the thyroid in a 3 mm. hindlimb length stage. 

 Note the homogeneous dense colloid and the heavy, compact Golgi material. 

 (Bottom) A large follicle of the thyroid of the forelimb emergence stage. Colloid 

 shows areas of various densities. Higher epithelium contains material showing 

 definite network and extensive ramification. (From S. A. D'Angelo & H. A. 

 Charipper, J. MorphoL, 64:355.) 



