502 



PATTEN AND HAZEN. 



c. Cross-section through a hollow cell. d. Section through a granular cell. 

 e. Section through a triangular cell filled with granules. 



Fig. 8o. Cross-section through the end sac of a specimen in the Trilobite 

 stage. The section is posterior to the point where the nephridial duct opens into 

 the end sac. The end sac is lined with small and finely granular cells. One large 

 cell is shown on the dorsal side of the sac, filled with small granules, and with 

 pseudopodia extending out from its free margins. At the lateral side the end sac 

 shows a projection similar to both the wall of the end sac, and to the long hollow 

 cells which are characteristic of this age. Ventral to this sac is another of similar 

 structure, which unites with the end sac in the second section posterior to this. 

 These projections are either outgrowths from the wall of the end sac, or nephrid- 

 ial tubules united with it. Scattered among the nephridial cells were a number 

 of small red cells. Some of them had a faintly granular protoplasm, others were 

 vacuolated, and still others in which nothing but the cell walls could be distin- 

 guished outside the nucleus. X 400. 



Fig. 81. Drawing of the injected nephric duct of an adult Limulus from the 

 dorsal side. The main part of the duct is coiled and folded upon itself many 

 times, the distal arm alone remaining straight, running from a point in front of 

 the anterior transverse process of the plastron along the edge of the plastron as 

 far as the fourth nephric lobe. It then passes between the muscles through the 

 median end of the last nephridial lobe to the exterior. Along the free margin of 

 the duct, slight projections, or pockets (/''•), are found. In other places small 

 connecting tubes (<r.A) unite different portions of the duct. 



Fig. 82. In this case the duct has been dissected apart along its entire length. 

 In many places small tubes were found, connecting one fold of the duct with 

 another which lay either beneath or beside it. In most cases these connecting 

 tubes had to be cut in order to free and unfold the duct. A few of them are left 

 untouched {c.n.t.). In other places small evaginations or pockets in the wall of 

 the duct were found along its free margin {po.). The nephric duct lies below the 

 outer edge of the plastron, deeply imbedded in muscle, the genital organs, and in 

 the hepatic caeca. The fourth lobe of the Nephridia shows from below. 



Fig. 83. Drawing of the nephric region of an adult Limulus, showing the 

 nephric duct, nephridial lobes, and the blood vessels and nerves. 



The four nephridial lobes lie at the base of the second, third, fourth, and fifth 

 legs. They are connected along their median dorsal ends by a band of collecting 

 tubes — the stolon. A short distance from the oral ring small branches arise from 

 the pedal arteries of the second, third, fourth, and fifth legs, and pass along the 

 ventral surface of each of the nephridial lobes, supplying the muscles beyond. 

 During its course, each artery sends off alternate branches to the muscles and to 

 the lobe. The arteries which pass to the lobes break up into small branches, 

 which fill the nephridia with a network of vessels. 



Large integumentary nerves {int.n.), arising from the haemal side of the brain, 

 pass out between each nephridial lobe to the sides of the carapace. On either side 

 of each lobe a smaller nerve arises from the haemal side of the pedal nerve which 

 supplies the tergo-coxal and the plastro-coxal muscles on the posterior and anterior 

 sides of the base of the coxite. The nephric duct lies near the lateral dorsal side 

 of the lobes. The distal arm passes through the posterior median end of the 

 fourth lobe to the external opening at the base of the fifth leg. The ectodermic 

 portion of the duct extends from the external opening to the fourth lobe. 



