unio prolium

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
UNIO PROLIUM. A species of adoption used among the Germans; it signifies 
union of descent. It takes place when a widower, having children, marries a 
widow, who also has children. These parents then agree that the children of 
both marriages shall have the rights to their succession, as those which may 
be the fruits of their marriage. Lec. Elem. Sec. 187. 
    

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