PLATE 5 



EXPLANATION OF FIGURES 



20 Transverse section through the parathyreoid IV and the caudal portion 

 of the thymus of the right side of an embryo Chelydra with carapace 16 mm. long. 

 X 50. 



21 Same embryo. Section through parathyreoid III and the thymus of the 

 right side. X 50. 



22 Same embryo. Section taken farther anteriorly than that of figure 21, 

 showing thymus and parathyreoid III of left side. X 50. 



23 Transverse section through the ultimobranchial body and the para- 

 thyreoid IV of the left side; from same embryo as figures 20 to 22. X 75. 



24 Transverse section through the left ultimobranchial body and the para- 

 thyreoid IV of an embryo Chrysemys at hatching. X 50. 



32S 



