Only men are allowed to be Priests (and no transgenders allowed).  They take a vow of celibacy.  A priest participates in priesthood after the Sacrament of Holy Orders, he acts in persona Christi Capitis, representing the person of Christ.  Only Priests can perform the ceremony of the Eucharist, which derives from the story of the Last Supper,

As of December 31, 2014, there were 415,792 Catholic priests worldwide, decreased 5,000 since 1970.  The worldwide Catholic population has nearly doubled, growing from 653.6 million in 1970 to 1.229 billion in 2012.

ORDINATION CEREMONY

The candidates lie prostrate before the altar, while the assembled faithful kneel and pray for the help of all the saints in the singing of the Litany of the Saints. The essential part of the rite is when the bishop silently lays his hands upon each candidate (followed by all priests present), before offering the consecratory prayer, addressed to God the Father, invoking the power of the Holy Spirit upon those being ordained.

The Priest’s Collar     (similar to a dog collar)