PLATE 4 



EXPLANATION OF FIGURES 



14 Photomicrograph of a section through the anterior thymus (thymus III) 

 and the anterior parathyreoid gland (parathyreoid III) of an adult Chrysemys 

 picta. On the left is a part of a thymic lobule, showing dense cortex and lighter 

 medulla, the latter containing thymic corpuscles. On the right is the parathy- 

 reoid gland. Haematoxylin and eosin. X 100. 



15 Photomicrograph of a section through the left aortic body of an adult 

 Chrysemys picta, to show the postbranchial body, the posterior thymus (thymus 

 IV), and the posterior parathyreoid gland (parathyreoid IV). The crescent- 

 shaped mass in the upper half of the section is the postbranchial body. Below 

 and on the left is the posterior parathyreoid gland; on the right is the posterior 

 thymus. Haematoxylin and orange G. X 66. 



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