. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. OVUM. [121] puscles; which are held by Nelson thus to pene- trate or gain access to the vitelline substance. E. Ovum more advanced ; the vitelline and albuminous membranes formed; clear highly re- fracting spaces resembling altered spermatic cor- puscles are seen in the yolk substance. F. Ovum after fecundation; uniform structure of the yolk substance previous to the appearance of the embryonic cell and commencement of segmenta- tion. The chorion has now become tuberculated. of the ova appears to consist, first, in the p
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. OVUM. [121] puscles; which are held by Nelson thus to pene- trate or gain access to the vitelline substance. E. Ovum more advanced ; the vitelline and albuminous membranes formed; clear highly re- fracting spaces resembling altered spermatic cor- puscles are seen in the yolk substance. F. Ovum after fecundation; uniform structure of the yolk substance previous to the appearance of the embryonic cell and commencement of segmenta- tion. The chorion has now become tuberculated. of the ova appears to consist, first, in the production of minute cell-germs in the upper- most part of the ovarian tube immediately adjoining its coecal termination. It does not appear to be fully ascertained whether these germs are originally, as some have supposed, the maculae or nuclei, or rather, as others hold, the germinal cells or vesicles themselves : the latter opinion appears to be the most probable. Second, the granules of the yolk-substance very soon collect round the exterior of the ger- minal vesicles. These granules appear at first to be suspended in fluid ; but a little later, as they come to collect round the germinal vesicles, they are united together in a mass by a firmer but clear basement substance, and when the minute ova have somewhat in- creased in size, the outline of this clearer basement substance of the yolk is distinguish- able. There is not, however, at first any ex- ternal or vitelline membrane; of this Dr. Nelson and I have convinced ourselves by re- peated observations in Ascaris mystax.* The ova, as they continue to descend in the vitelligenous part of the tube in immense numbers closely pressed together, assume the form of subtriangular flattened bodies, and come to be arranged in series of three, four, or more, in a short spiral round the centre of that part of the ovarian tube which constitutes the yolk organ, as round a central axis, but without being united together by any com- mon
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