312 



PA TTEN. 



[VOL. I. 



The glandular portion of the kidney is developed from six 

 pairs of segmentally arranged "anlagen." Omitting all details, 

 it may be stated that a part of the fifth coelomic cavity persists 

 as the thin-walled chamber or end sac mentioned above. The 

 other coelomic cavities of the thorax break down after produc- 

 ing, by a thickening of their neural walls, paired masses of finely 

 granular cells. These cells become hollow and unite end to 

 end to form irregular groups of anastomosing tubules. The 



c 



FIG. i. Diagram of the excretory organs of an immature Limulus. 



tubules derived from the walls of the first and sixth coelomic 

 cavities disappear. The remaining ones form the four lobes of 

 the adult kidney. The longitudinal tubules of the stolon are 

 formed in a similar manner, by the union of outgrowths from 

 each cluster of cells. Many tubes on the periphery of the 

 gland retain the embryonic condition in the adult. But in the 

 center of the lobes and in the longitudinal stolon the nuclei 

 of the tubules multiply rapidly, giving rise to a lining endothe- 

 lium of flattened cells. 



