. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. [126] OVUM. lated condition of the ovum in the ovary, that it is in fact the remains of the divided pedicle after the ovum is separated from the place of its original formation. Fig. 91*.. Ovum and Mlcropyh in Holothuria tubulosa. (From Ley dig.) a, b. A small portion of the ovary from the inner surface, containing ova in various earlier stages of their development; three of them project from the inner surface, of which a is the most de- veloped. In this one the pediculated attachment and enclosure of the ovum by the nuc
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. [126] OVUM. lated condition of the ovum in the ovary, that it is in fact the remains of the divided pedicle after the ovum is separated from the place of its original formation. Fig. 91*.. Ovum and Mlcropyh in Holothuria tubulosa. (From Ley dig.) a, b. A small portion of the ovary from the inner surface, containing ova in various earlier stages of their development; three of them project from the inner surface, of which a is the most de- veloped. In this one the pediculated attachment and enclosure of the ovum by the nucleated ovarian membrane is seen, the yolk granules and the ger- minal vesicle with its macula. c. A more advanced ovum now separated from the ovary. Externally the nucleated remains of the ovicapsule are represented ; inside this the thick albuminous layer marked with radiated lines, and lined closely by the vitelline membrane; both these, as well as the ovicapsule, being perforated by the micropyle formed at the place where the pedicle formerly existed. The micropyle aperture has also been ob- served in other Echinodermata, viz. by J. Miiller in Ophiothrix fragilis, in which he states its diameter to be y^n/'* anc* nis son Max Miiller in Sternaspis thalassemoides.* This aperture has not yet been observed in the ovum of Echinus. In the fecundated ova of this genus, however, Derbcs observed spermatozoa to have passed through the thick external albuminous covering, but not within the more delicate vitelline membrane; but in this animal the external covering is more like a layer of soft albumen than a dense mem- brane as in Holothuria. The ova of Echinodermata take their origin, like those of other animals, by the formation of the germinal vesicles. These have been * The micropyle was represented in the ovum of Holothuria txibulosa by R. Wagner in his Icones Zootomicffl, tab. xxxii., fig. 12., before its nature was known. The first discovery of a micropyle in the animal ovum
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