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770 water. When this tube has been extruded an inch or thereabouts, it suddenly fills with an opaque whitish material, ruptures and collapses, the fluid spreading over the surface of the erosion. If a little of the fluid, either that which has welled up through

Fig. 150.—Embryos of D. medinensis. (Microphotograph by Mr. H. B. Bristow.)

the hole, or that which has escaped from the ruptured tube, is placed under the microscope, it is seen to contain myriads of dracunculus larvæ lying coiled up, almost motionless, with their tails projecting in a very characteristic manner (Fig. 150). If now a drop of water be instilled below the cover-glass the larvæ