LIMULUS POLYPHEMUS. 



495 



INDEX LETTERS TO PLATE XXV. 



<7/.^* = the second to the sixth ap- 

 pendages, respectively. 

 ant.n.d. = anterior arm of the nephric 

 duct. 

 b.r. = brain. 

 d.s. = blood space. 

 d.v. = blood vessel. 

 c.n.c. = cross-section through ne- 

 phridial cell. 

 e.s. = end sac. 

 ex.n.d. = nephric duct near the external 

 opening. 

 g.c. — granular cells. 

 g.n.c. — granular nephridial cells. 

 g.t. — tubules lined with granule 

 cells. 



l.n.c. = longitudinal section through 

 nephridial cells. 

 n.c}-^ = nephridial cells in the first 

 to the sixth append- 

 ages, respectively. 

 n.c. = nephridial cell. 

 ?t.d. = nephric duct. 

 n.P,n.l.*= third and fourth nephridial 

 lobes. 

 n.t. = nephric tubules. 

 oe. = oesophagus. 

 //. = plastron. 

 post.n.d. = posterior arm of the nephric 

 duct. 

 r.c. = red cells. 

 a.t. = areolar tissue. 



EXPLANATION OF PLATE XXV. 



Fig. 43. Longitudinal sections through the second to the sixth legs of an 

 embryo a little younger than the Trilobite stage. The chelicera have remained 

 near the median line, so that they are not included. Bunches of nephridial cells 

 are seen at the base of the second, third, fourth, and sixth legs, and the nephric 

 duct in the fifth leg. X 100. 



Fig. 44. A transverse section through the region of the second, third, and 

 fourth legs of the Trilobite stage. Nephridial cells are seen at the base of the 

 third and fourth legs. The duct has grown anteriorly nearly as far as the second 

 leg, and both the distal and proximal limbs are shown in the figure. X 100. 



Fig. 45. Enlarged drawing through the dorsal region of the fourth and fifth 

 legs from the same series as Fig. 44, showing the nephric duct and the nephridial 

 cells in various stages of development, x 400. 



Fig. 46 . Horizontal section through the fourth and fifth legs of a specimen in 

 the second larval stage. As the section was cut near the external opening of the 

 duct, only one portion of it is seen. The nephridial lobes form a definitely marked 

 area, and the portions in the second, third, fourth, and fifth legs have united with 

 one another. The nephridial lobes are composed of a lacuna tissue, in which are 

 large granular cells of varying sizes. X 200. 



Fig. 47. Cross-section through the fourth leg of a younger specimen of the 

 second larval stage than the preceding one. The dorsal side of the section is on 

 the right. The nephric duct is much coiled, and several sections through it are 

 shown. Cylindrical cells with fine granules around the periphery are uniting end 



