Explanation of Plate I

All figures except Figs. 1 and 2 were drawn with the aid of a camera lucida. The projected scale has the indicated value in mms. Abbreviations: ac, acetabulum; cm, cellular mass; f, flame cell; gc, gland cells; gp, genital papilla; ov, ovary: t, testis: up, uterine pore; ut, uterus; vt, vitellaria.

• Fig. 1.—Diagram of adult specimen of Gyrocotyle rugosa. Ventral view.
• Fig. 2.—Diagram of the pointed or spined papillae on the ridges of the body surface of G. rugosa. Greatly enlarged.
• Fig. 3.—Egg of G. rugosa. From terminal coils of the uterus.
• Fig. 4.—Shell of a hatched egg, showing operculum.
• Fig. 5.—The lycophore larva of G. rugosa. Semi-diagrammatic.
• Fig. 6.—A single hook of the lycophore larva.
• Fig. 7.—Hooks of an eight-hooked lycophore crushed to spread the hooks.page 11
• Fig. 8.—Flame cell from the lycophore larva.
• Fig. 9.—Young juvenile or postlarval stage of G. rugosa from scrapings of the mucosa of the spiral valve of the elephant fish.
• Fig. 10.—Posterior end of a somewhat larger juvenile stage.
• Fig. 11.—Lycophore larva of G. rugosa in a blood vessel in the wall of the spiral valve of the elephant fish. From a 10-micron section of a piece of tissue exposed to free-swimming lycophore larvae.