LIMULUS POLYPHEMUS. 487 



in the second, third, fourth, and fifth legs form the four lobes 

 of the adult organ. Offshoots extend forward and backward 

 from the median end of each lobe, that unite with each other 

 and with the end sac to form the longitudinal ducts of the 

 stolon. The nephric cells of the first and sixth somite disap- 

 pear. In the stolon, and in the larger tubules on the dorsal 

 side of each lobe, the nephric cells become flattened, and by 

 repeated divisions are finally converted into a pavement epi- 

 thelium, thus changing the intracellular lumina into intercel- 

 lular ones. New tubules are formed throughout life by the 

 transformation of indifferent cells on the ventral surface of 

 each lobe. 



