LIMULUS POLYPHEMUS. 



501 



INDEX LETTERS TO PLATE XXVIII. 



c.n.t. = cross-section through a nephrid- 

 ial tubule. 

 c.t. = connecting tubes. 

 ec.p. = ectodermic part of nephric 

 duct. 

 e.s. — end sac. 

 e.s.t, = tubule of the end sac. 

 ex.0. = external opening of the nephrid- 

 ial duct. 

 ^.c. = granular cells. 

 A.f.^. = hollow cells forming tubules. 



l.r.c. = large red cells. 

 mus. = muscle. 

 ii.l}-* = nephridial lobes. 



p.a. = pedal artery. 



//. = plastron. 

 p.n. = pedal nerves. 



fo. = pockets in the 

 duct. 



r.c. = red cells. 



v.c. — vacuolated cells. 

 s.r.c. = small red cells. 



walls of the 



EXPLANATION OF PLATE XXVIII. 



Fig. 74. A few characteristic nephridial cells of the Trilobite stage, a. Longi- 

 tudinal section through a cell with finely granular protoplasm around the periphery. 

 As the section passes near the surface of one end of the cell the granules show a 

 reticulated arrangement, b. A cross-section through two cells similar to a. The 

 nucleus adheres to the side of the cell. c. Shows a small red cell on the surface 

 of b. d. Red cells, with a clear protoplasm which took a deep stain in Lyon's 

 blue. X 475- 



Fig. 75. Sections through the nephridial cells from one of the older specimens 

 of the second larval stage, a. Longitudinal section through a tubule, b. Cross- 

 section through a tubule, c and d. Cells in which large, dense-looking granules 

 cover the nucleus. X 475. 



Fig. 76. Cross-section through the region on the dorsal side of the heart of 

 Limulus in the second larval stage, showing hollow cells similar to those in the 

 nephridial lobes. Several cells have united end to end to form branching tubules. 

 Other cells are present filled with large granules (^.^.), while others of the same 

 size have only a few granules in them. X 300. 



Fig. 77. Section through a granular cell of a young Limulus three-fourths of 

 an inch long. (See PI. XXIII, Fig. 48.) It shows one enormous granule in the 

 center with smaller ones around it. X 475. 



Fig. 78. Section through nephridial cells, from the younger specimens of 

 the second larval stage, a. Longitudinal section through tubules which show a 

 granular periphery, b. Section through two cells which have united, c. Cross- 

 section through a tubule, d. A small cell with the nucleus surrounded by 

 granules. X 475. 



Fig. 79. Section of cells in the sixth leg of a specimen in the second larval 

 stage. X 475. a. Long hollow cells uniting, similar to those in the nephridial 

 and pericardial regions of the same age. b. Large triangular cells uniting. 



