108 EARLY EMBRYOLOGY OF THE CHICK 



VII. THE URINARY SYSTEM 



In the section-diagrams of Figure 36, D and E, certain parts 

 of the urinary system which have been established in chicks of 

 50 to 55 hours will be found located and labeled. The urinary 

 system is relatively late in becoming- differentiated. Only a 

 few of the early steps in its formation can at this time be made 

 out. Many structures which later become of great importance 

 are not represented even by primordial cell aggregations. Ex- 

 cept for those well grounded in comparative anatomy, any 

 logical discussion of the structures which have appeared must 

 anticipate much that occurs later in development. Consider- 

 ation of the mode of origin and significance of the nephric 

 organs appearing at this stage has, therefore, been deferred. 



