PLATE 2 



EXPLANATION OP FIGURES 



8 a, 8 b, and 8 c From photographs of transverse sections through near the 

 anterior, middle, and posterior portions respectively of the tripartite complex, 

 showing the gradual enlargement of the ultimobranchial bodies from their an- 

 terior to their posterior ends. The posterior end of the tripartite complex is 

 largely composed of the ultimobranchial bodies. From an embryo 23 mm. long. 

 X 60. 



9 From a photograph of a transverse section about midway between the two 

 ends of the tripartite complex showing the ultimobranchial bodies largely broken 

 up into coarse cell cords. From an embryo 27 mm. long. X 56. 



10 a, 10 b, and 10 c From photographs of transverse sections through the 

 anterior, middle and posterior portions respectively of the tripartite complex. 

 The ultimobranchial body on the left side extends along the posterior three- 

 fourths of the thyroid gland while the right one along only its posterior fourth. 

 The unecjual size of the two ultimobranchial bodies, which are largely broken up 

 into coarse cell cords, produce the asymmetry of the tripartite complex. From an 

 embryo 29.5 mm. long. X 56. 



11 a and 11 b From photographs of sections through the anterior and nearly 

 the middle portions respectively of the tripartite complex showing both ultimo- 

 branchial bodies separated from the anterior portion of the thyroid gland (fig. 

 11 a) and the left one with traces of the lumen also separated from the thyroid 

 (fig. 11 b). From an embryo 48 mm. long. X 60. 



Ep.B., epithelial buds Tr., trachea 



L., lumen U., ultimobranchial body 



T., thyroid gland 



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