180 



FOUNDATIONS OF BIOLOGY 



further complicated by anatomical, though not physiological, 

 relations with the reproductive system. As will be pointed 

 out later, this neighboring system now and again foists, as it 

 were, some of its accessory responsibilities upon parts of the 



FIG. 98. Longitudinal section of the human kidney. Ct, cortex, or region in 

 which the essential nephridial elements, the tubules, come into functional asso- 

 ciation with the capillaries; M, medullary portion, through which the tubules 

 extend to open on the summits of the pyramids (Py); P, pelvis of kidney; Ra, 

 renal artery; U, ureter. (After Huxley.) 



excretory (urinary) system, and even takes over portions and 

 makes them integral parts of its own when they have been 

 permanently abandoned by the urinary system in its evolu- 

 tionary development. 



