Page:Popular Science Monthly Volume 14.djvu/655

Rh seen in the figure. When in the natural position these projections lie within the "sheath" (D). These are known as the stop-valves. The tubes of the lancets terminate just back of where the stop-valves are attached, here opening into the cylindrical portion of the "sheath."



We pass now from the lancets to the "sheath" (Fig. 1, D), The general shape is well shown in the figure. The cylindrical portion (D) suddenly contracts, forming a shoulder at d, and a slender portion extends for some distance beyond. Along the straight edge the lancets