No. 3] LIMULUS POLYPHEMUS. 485 



The last-named cells may be found in the second larval stage 

 distributed throughout the nephridial lobes (PL XXV, Fig. 47, 

 g.c), and they occur in large masses along their lateral margins. 

 These cells are round or oval, and are filled with great num- 

 bers of coarse granules, which usually completely conceal the 

 nucleus. They are well shown in PL XXV, Fig. 46, g.c, and 

 PL XXVIII, Fig. 75,^.^. 



In larvae three-quarters of an inch long the cells on the 

 lateral margins of the lobes are enormous (PL XXV, Fig. 48, 

 and PL XXVIII, Fig. 'j'j). Similar cells were found through- 

 out the body, from the proventriculus to the first gill. In the 

 anterior sections they are most numerous on the dorsal and 

 lateral sides of the proventriculus. They also extend laterally 

 on the ventral side of the body close to the ectoderm. Pos- 

 terior to this they are less abundant around the alimentary 

 canal, but are thickly massed around the base of the legs. In 

 the sixth leg and in the operculum they are more numerous 

 than in any other place. Similar cells are found in the region 

 of the heart. The origin and fate of these cells were not 

 determined with certainty. They agree in some respects with 

 the granular cells seen in the early stages of the nephric lobes, 

 and which, as we have seen, subsequently cleared up and 

 formed the nephric tubules. 



During the Trilobite and second larval stage, cells are found 

 in the pericardial region that closely resemble nephridial cells. 

 They are most abundant on the dorsal side of the pericardium 

 in the sixth thoracic segment and over the proventriculus. Many 

 cells are hollow and united end to end, forming loose-branching 

 tubules like those in the nephridial lobes of the Trilobite stage 

 (PL XXVIII, Fig. ^6, h.c.t). Among these cells are a few of 

 the large granular ones (g.c.^), and some of the small dark red 

 cells (r.c.) like those seen in the nephridial lobes. All these 

 cells probably arose from the nephridial "Anlagen" at the base 

 of the legs, and were carried to their present position by the 

 growth of the somites over the dorsal surface of the egg. 



The same kind of cells are also found in the chelicerae and 

 in the sixth leg. Those in the cheliceral segment (PL XXIV, 

 Fig, 40) disappear early. Those in the sixth leg appear before 



