No. 3.] LIMULUS POLYPHEMUS. 477 



slipper-shaped outline. This is the growing surface of the lobe, 

 and contains just beneath the outer layer the finest tubules and 

 capillaries. The median side of the lobe is somewhat wedge- 

 shaped, the coarsest ducts being nearest the apex of the wedge. 

 At the ventral ends of the lobes the wedge-shaped surfaces 

 gradually widen, as the coarser tubules diverge to meet those 

 forming the stolon uniting the four lobes. The network of 

 coarse longitudinal ducts of the stolon empty into the end sac 

 situated in the middle of the fifth lobe ie.sJ), and from there 

 the secretions pass to the exterior through the long nephric 

 duct. 



The size and outline of the different lobes, especially the first 

 one, vary a good deal in different individuals. 



The nephric gland lies deeply imbedded in the muscles 

 around the base of the legs, and can be readily recognized in 

 the fresh condition by its brick-red color. In some specimens 

 the surface is a pale yellow, or is mottled with red patches. 

 The inside of the lobes, however, was always brick red. Each 

 nephridial lobe had two ear-like lobules attached to its median 

 ventral end near the stolon. On the first lobe they were large, 

 massed one above the other, and entirely covering the collect- 

 ing tubes. On the remaining lobes they were much smaller, 

 and were connected with them by a slender stalk. 



A short distance from where the pedal arteries leave the 

 circum-oral ring a large blood vessel arises which extends lat- 

 erally along the posterior ventral margin of each nephric lobe. 

 It passes directly through the median portion of each lobe to 

 supply the muscles and other tissue beyond. Before entering 

 the nephric lobes many branches are given off, the anterior 

 ones supplying the nephric lobes, the posterior ones the adja- 

 cent muscles. These blood vessels form a rich mass of capil- 

 laries round the nephric tubules. 



Nerves. — Two sets of nerves pass close to or through the 

 nephric glands. The haemal, or integumentary, nerves of 

 the third, fourth, and fifth thoracic neuromeres pass through 

 the stolon, and between the nephric lobes, to the sides of the 

 carapace, without apparently giving off any branches to the 

 gland (PI. XXVIII, Fig. 83, int.n., and PI. XXVI, Fig. 49, n). 



