18 Transverse section showing the now much reduced finger-shaped first thy- 

 mus body (ti) of the 10 mm. larva. It protrudes dorsally from the pharynx and 

 reaches almost to the ventral surface of the facial ganglion, which lies just a1)0ve 

 jt in this region. (X 50) 



19 The same thymus body enlarged (X 200), showing large epithelial cells 

 similar to those of the pharynx. It is connected directly with the pharj^nx by a 

 islightly constricted stalk. 



20 Transverse section showing the postbranchial body of 10 mm. larva. 

 (X 50) 



21 Transverse section through the fifth thymus body of 11 mm. larva. 

 (X 50) 



22 Section through the fifth thymus body of 11 mm. larva much enlarged 

 (X 200) , showing the large epithelial cells imbedded in the surrounding connective 

 tissue. 



23 Transverse section through the anterior region of the thyreoid gland of a 

 19 mm. larva, showing the position of three thyreoid follicles placed about the 

 dorsal wall of the inferior jugular vein. The external carotid artery is somewhat 

 dorso-lateral. (X 95) 



24 Section showing the three thyreoid follicles of figure 23, in more detail. 

 (X 200) 



25 Transverse section showing the relative position of the postbranchial 

 body, (pb.) of 19 mm. larva. (X 50) 



26 Transverse section through the third thymus body (^m) of a 19 mm. 

 larva. (X 50) 



676 



