. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. OVUM. [83] Fig. 56*.. Ovum of the Rabbit in the tunica granulosa. (From Cos/e.) The middle part of one of M. Coste's figures has been here copied to show the peculiar arrangement of the granular cells round the disc and ovum, which according to him are of the same nature with those described by Dr. Martin Barry as retinacula. It may be doubtful whether this structure is constant. and bears no regular proportion in different families of animals to the stature of the whole body. In the mature state this variation ex- tends
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. OVUM. [83] Fig. 56*.. Ovum of the Rabbit in the tunica granulosa. (From Cos/e.) The middle part of one of M. Coste's figures has been here copied to show the peculiar arrangement of the granular cells round the disc and ovum, which according to him are of the same nature with those described by Dr. Martin Barry as retinacula. It may be doubtful whether this structure is constant. and bears no regular proportion in different families of animals to the stature of the whole body. In the mature state this variation ex- tends from TA<J to 2<ro or Ho''- The Allowing are the results of a few measurements made by myself and others of the external diameter of the mature ovarian ovum, viz., man T£^, dog T|o, cat T-b-, rabbit ^0, ™t ^, mouse ^, pig 25o. cow ulo' guinea-pig TV'-. The external tunic, or zona pellucida (a term founded on the description of Von Baer*, from its presenting the appearance of a transparent ring between the opaque granular yolk-mass within and the granular cells externally), is of great proportional thickness ; viz., from -^-so-a to ^sVo". or fr°m i to TV °f the whole diameter of the ovum. When entirely freed from the granular cells, its external surface appears smooth ; and the inner surface, which is exactly parallel to the outer, is also re- markably smooth. The substance of this tunic is very tough, and possesses considerable elasticity; so that the ovum and its zona may be flattened by external pressure to a great extent ; and yet it regains its nearly spherical form when the pressure is removed. It is of glassy transparency and homogeneous ; neither any laminated, nor fibrous, nor other structure being perceptible under the highest magnify- ing power. It is easy to obtain evidence that it is one thick membrane, and not composed of two layers with intervening fluid, as some have held, by cleaving it with fine needle- points, when the cut edge becomes fully a
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