See English Rules Under the Judicature Act (The Annual Practice, 1937) O. 16, r. 11. See also [former] Equity Rules
43 (Defect of Parties—Resisting Objection) and 44 (Defect of Parties—Tardy Objection).
For separate trials see Rules
13
(i) (Counterclaims and Cross-Claims: Separate Trials; Separate Judgments), 20(b) (Permissive Joinder of Parties: Separate Trials), and 42(b) (Separate Trials, generally) and the note to the latter rule.
The language of Rule
21 has been amended as part of the general restyling of the Civil Rules to make them more easily understood and to make style and terminology consistent throughout the rules. These changes are intended to be stylistic only.