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Show 292 MR. J. T. CUNNINGHAM ON THE [May 4, EXPLANATION OF THE PLATES. PLATE XXVIII. Explanation of lettering : /, follicular epithelium ; v.m, vitelline membrane ; z.r, zona radiata ; g.v, germinal vesicle ; b.v, blood-vessels ; g.c, germinal colls ; e, superficial germinal epithelium; c, cells in interior of ovum; y, yolk-masses. Fig. 1. O v u m of Lepidosiren (Protopterus) before commencing formation of yolk. 2. Ovum of Lepidosiren {Protopterus), to show the commencing formation of yolk. 3. Ovum, with cells in interior. 4. Nearly mature ovum, to show differentiation of yolk into a peripheral and central portion and modification of germinal vesicle. 5, 6. T w o ova, belonging to tbe same series as fig. 3, to show the proliferating follicular cells. 7. Early stage in development of ovum, represented in figs. 3, 5, 6, to show the central mass of germinal cells which, at x, have commenced to fuse, and the invaginated mass of cells which form the follicular layer: o, immature ovum belonging to series represented in figs. 1, 2, 4. P L A T E XXIX. Fig. 1. Germinal vesicle of ovum (Plate XXVIII. fig. 4), more highly magnified, to show its specialization into an outer and inner layer: n, germinal spots. 2. A portion of ovum (Plate XXVIII. fig. 1), more highly magnified. 3. Germinal vesicle of same ovum, highly magnified, superficial view : n, germinal spots. 4. The same, in section; lettering as before. 5. Portion of ovum a little more mature than that shown in Plate XXVIII. fig. 2. 6. Nearly mature ovum. 7. Less mature ovum of same series as last, to show the follicular epithelium resting directly upon the contents of the ovum; y, yolk-particles in follicular cells. 8. Very young ovum. 9-20. Cells from interior of ovum (Plate XXVIII. fig. 3), showing various conditions of division and degeneration : y', yolk-particles in interior of cell; n, their nucleus ; y, yolk of ovum. 3. On the Mode of Attachment of the Ovum of Osmerus eperlanus. By J. T. CUNNINGHAM, B.A., F.R.S.E., Fellow of University College, Oxford, and Superintendent of the Scottish Marine Station. (Communicated by Mr. F. E. BEDDARD.) [Eeceived April 20, 1886.] (Plate XXX.) In several works on Ichthyology and Pisciculture it is stated that the ovum of the Smelt is adhesive. The mode of attachment is described as differing from that which occurs in the Herring-ovum iu the following manner :-In the Herring-ovum the whole of the outer surface of the egg-membrane at the moment of deposition is glutinous, and the ovum becomes attached at any part of the surface |
