880 



SKIN STEUCTUEE AND EXCRETION 



by branching blood vessels. Its action is as follows . The 

 waste from the body cells of the segment collect in the 



ex.p 



Fig, 176 — Cross section of earth worm showing nephridia in position; B. C, body 

 cavity; c, cutis; e, epidermis; c. m. & I. m. muscle layers; X, nephridia; ex.p. 

 excretory pores; S, seta^; Z>, dorsal blood vessel; Z, intestine; F, ventral blood 

 vessel; ^. V., ventral nerve cord. 



cavity or are absorbed into the blood circulation. Those 

 wastes of a nitrogenous character which remain in the cav- 

 ity of the segment pass directly into the ciliated end of one 

 or the other of the nephridia, and, after action by the cells, 

 pass out of the pore as a secretion. Similarly, the wastes 

 which entered the blood are eventually brought to the 

 branches which surround this tube, and, being absorbed 

 from the blood by the secreting cells, are made into a secre- 

 tion, and in turn pass down the duct and out the pore. In 



