This section is from the book "Popular Law Library Vol7 Equity Jurisprudence, Trusts, Equity Pleading", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
There is not the same hard and fast division between parties complainant and defendant in equity as between plaintiffs and defendants at common law. In equity if a person who would properly be a complainant refuses to join with the other parties having a common interest with him he may be made a defendant. We thus see that in equity parties with the same interest may be (in form) on opposite sides of the case, while one defendant may be seeking relief from another defendant. A party made a defendant in a bill may file a cross bill asking relief against another defendant.
4 Shipman on Equity Pleading, Sec. 14.