-47- 



and two lateral parts. The median lamella is no longer a com- 

 plete partition and shows a decided swelling on its dorsal edge. 

 (Mag. 240 diam. ) 



Pig. 5 j. Transverse section a short distance poste- 

 rior to the opening of the duct. The cllisted groove is still 

 present but much diminished in depth. (Mag, 240 diam.) 



Fig, 5 k. Transverse section posterior to Fig. 5 j 

 passing through the beginning posterior coll. Khows the now 

 broad and shallow ciliated groove close to the top of the gland, 

 and the ciliated dorsal ridge on the roof of the pharynx. 

 (Mag. 240 diam. ) 



Fig. 5 1. Transverse section through the extreme pos- 

 terior end of the gland, (Llag, 240 diam.) 



Fig. m. A horizontal section through the thyroid, 

 showing the extent of the complete median lamella, the relative 

 position of the visceral arches, etc. (Ivlag. 240 diam.) 



Fig. 6 g. Transverse section through the anterior end 

 of the thyroid of a lOom. -^ gtromj -s^r larva. All four groups of 

 cells are now fully developed, and the gland has increased great- 

 ly in size, as is sho'Wi by the fact that Figs. 5 a-m were magni- 

 fied 240 diameters, while the larger Figs. 6 a-1 were magnified 

 only 90 times. This figure about corresponds to Fig, 5 e of the 

 preceding stage. 



Fig, 6 b. Transverse section posterior to Fig. 6 a 

 and just anterior to the opening of the duct. Corresponds to 

 Fig, 5 h of the preceding stage, (Wag, 90 diam,) 



