In most Catholic churches the tabernacle is constructed to resemble a house. This reflects the basic symbolism that it "houses" Jesus, truly present under the appearances of bread.
However, in some places a tradition was established of constructing tabernacles within statues of the Virgin Mary.
Father Stefano Manelli in his book, Jesus Our Eucharistic Love, briefly explains this tradition.
[I]n some of the churches in France, the tabernacle used to be encased in a statue of Our Lady of the Assumption. The significance is quite clear: it is always the Blessed Virgin Mary who gives us Jesus, who is the blessed Fruit of Her virginal womb and the Heart of Her Immaculate Heart.
More recently a unique monstrance was constructed for St. Stanislaus Kostka Parish in Chicago that possessed similar imagery.
It was called "Our Lady of the Sign - Ark of Mercy," and found its inspiration in the Ark of the Covenant found in the Bible.
The Ark of the Covenant was the visible sign of God’s presence, and his promise of Mercy, among the covenant community of Israel ... Turning to Mary pregnant with the child Jesus within her womb, she holds within her God’s promise of Mercy made flesh. She is the Ark of Mercy carrying the Law made flesh, the Bread of Life, and the High Priest within her to all people.
This idea of Mary being the new "ark" or "tabernacle" of God is a long tradition.
For example, the ancient Akathist hymn of the 6th century reads, "Hail! tabernacle of God and the Word. Hail! holy beyond all holy ones. Hail! ark gilded by the Holy Ghost. Hail! unfailing treasure-house of life."
Furthermore, Pope Benedict XVI reiterated this imagery in a homily on the feast of the Assumption.
Mary is the Ark of the Covenant because she welcomed Jesus within her; she welcomed within her the living Word, the whole content of God's will, of God’s truth; she welcomed within her the One who is the new and eternal Covenant, which culminated in the offering of his Body and his Blood: a body and blood received through Mary.
Therefore Christian piety rightly turns to Our Lady in the litanies in her honour, invoking her as Foederis Arca, that is, “the Ark of the Covenant,” the Ark of God’s presence, the Ark of the Covenant of love which God desired to establish with the whole of humanity, in Christ, once and for all.
While this tradition of constructing a tabernacle within a statue of the Virgin Mary is not widespread, it is an honorable custom that recognizes the beauty of Mary's role in salvation, and her image as the first "tabernacle" that housed the body and blood of Jesus Christ.
