BRANCHIAL DERIVATIVES IN TURTLES 301 



were to proceed in the same manner as in the case of the serpents, 

 then the first two, which represent the fourth and fifth pouches, 

 must develop into thymous tissue, while the third and hindmost 

 remains epithehal. But this does not occur; all three maintain 

 an epithehal character, and even in much later stages are 

 found in this condition, situated between the aorta and the 

 pulmonary arch. 



MATERIAL AND IMETHODS 



The present study is based upon a series of sectioned embryos 

 varying in size from 4 mm., greatest length, to newly hatched 

 specimens. The stains employed w^ere borax carmine and Lyon's 

 blue. Wax-plate reconstructions of the structures involved 

 were made from specimens of Chrysemys of 10 mm., greatest 

 length, and of 8 mm. carapace length (c. 1.) ; and from embryos 

 of Chelydra of lengths of 5 mm., 9 mm., and 9.5 mm. 



I am indebted to Dr. B. M. Allen for material to supplement 

 certain stages in my own series. 



The earlier part of the work unfortunately w^as undertaken 

 with very inadequate material and resulted in the erroneous 

 conclusion that the body closely associated during its develop- 

 ment with the ultimobranchial body was a derivative of the 

 fifth visceral pouch instead of the fourth. In the meantime there 

 appeared the work of Shaner- whose excellent models, especially 

 of a 9.5-mm. Chrysemys picta, leave no doubt as to the origin of 

 the body in question. While a corresponding stage is lacking 

 in my own material, I have a somewhat older specimen of Chely- 

 dra which proves the correctness of Shaner's results. 



THE VISCERAL POUCHES 



The account of the earlier stages in the development of the 

 visceral pouches is based upon embryos of Chelydra and of 

 Chrysemys. The conditions in the two genera are essentially 

 similar, and selection is made from one or the other accordingly 



2 R. F. Shaner, The development of the pharynx and aortic arches of the turtle, 

 with a note on the fifth pulmonary arches of mammals. Am. Jour. Anat., Nov., 

 192L 



