180 ABTHUB E. SHIPLEY. 



excretory cells. Some of the latter contain crystals, others large granules. 

 Only that part of the cuticle which is modified to form the horny plates is 

 shown. Between the plates and round the pore are pigment granules. 



Pig. 10. — A transverse section through the skin of the introvert and the 

 ventral nerve-cord. The introvert is retracted so that the outer surface is 

 concave, the inner convex. The section shows the conical papillae, the thick 

 cuticle with pigment granules, the single layer of ectoderm-cells, the continuous 

 layer of circular and longitudinal ujuscles, the latter broken only for the 

 insertion of the mesentery supporting the ventral nerve-cord ; and the peri- 

 toneal epitlielium. The nerve-cord shows the dorsal disposition of the nerve- 

 fibres and the ventral ganglion-cells. Some of the secondary nerves are cut 

 as they leave the cord and traverse the mesentery. 



Fig. 11. — A transverse section through both the external and internal 

 openings of the nephridium. The structure of the skin is shown, and four of 

 the circular nerves arising from the ventral nerve-cord are seen. The outer 

 wall of the nephridium is fused with the integument, but becomes free 

 posteriorly. The section does not show the whole of either opening, as they 

 do not lie wholly in one plane. 



Fig. 12. — A section through the integument. 



Mr. Wilson, of the Cambridge Scientific Instrument Company, has drawn 

 Figs. 1 and 5, and Figs. 4 and 7 are drawn from sketches made by Prof. 

 Weldon in Bimini. 



