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The pronephros of Chrysemys marginata. 



By 



T. H. Burleiid M. A., B.Sc. 



Assistant Lecturer and Demonstrator in Zoology at University College, Cardiff. 



With Plates 1-4 and 12 Fig. in the text. 



Introduction. 



The more important results of an investigation upon the early 

 development of the kidney in a species of American Terrapin — 

 Chrysemys marginata — have already been published (22), and in 

 the present paper I wish to deal with the subject in greater detail, 

 since my results tend to establish an undoubted homology between 

 the pronephros and mesonephros. 



Perhaps there is no subject upon which embryologists are more 

 divided than this question of the relationships between pro- and 

 meso-nephros. The period from about 1880 up to quite recently is 

 replete with literature dealing with investigations upon the onto- 

 geny of the urinary organ in vertebrate animals; and furthermore, 

 since these researches have led to the formulation of theories, often 

 diametrically opposed, later workers on the subject have usually 

 been under the disadvantage of having preconceived notions which 

 prevented them from giving an unbiassed judgment upon the obser- 

 vations which they may have made. 



The most prominent theoretical views at present held upon the 

 early development of the vertebrate kidney may be briefly set down 

 as follows. 



Zool. Jahib. XXXVI. Abt. f. Anat. 1 



