You have a list assignment in which the second slot, a typeglob, will be assigned the se second member of @_. *_ is the typeglob associated with the default variable "$_". In some cases where there are special properties (magic) bound to the underlying object (as in a tie for example) *_ is the thing to use to properly localize "$_".

It could also be that the author wanted to do a selective typeglob assignment; tough to say with so little code and of doubtful use for the variable _ (er.."$_").