What does Tarski mean here In Tarski's book Introduction to Logic page 30 he writes:
"Presumably only few are aware of the fact that such terms as 'equation', 'inequality', 'polynomial' or 'algebraic fraction', which are met at every turn in textbooks of elementary algebra, do not, strictly speaking, belong to the domain of mathematics or logic, since they do not denote things considered in this domain; equations and inequalities are certain special sentential functions, while polynomials and algebraic fractions--especially as they are treated in elementary textbooks--are particular instances of designatory functions"
I can understand saying they don't belong to the domain of mathematics, but I don't see why they are excluded from the domain of logic.  On page 6 he writes:
"Algebraic equations, on the other hand, that is to say formulas consisting of of two algebraic expressions connected by the symbol '=', are sentential functions."
But in the first quote, he speaks of "this domain" not "these domains."  
What's going on here?
For more context see:
Introduction to Logic
Equations as sentential fuctions
 A: He is alluding to the distinction between language and theory, form one side, and metalanguage and meta-theory, from the other:
From the point of view of modern logic, the (formal) theory of arithmetic is base on a language that uses expressions like :

$x < y \, $ or $\, \, x+y=1$.

The domain of the variables $x,y$ is "made of" the natural numbers.
Thus, the (formal) expressions like the one above "speaks of" numbers.
From this point of view, concept like equation, inequality, polinomial do not belong to the (formal) theory, because the variables and terms of the theory denote numbers and not expressions.
The concepts like equation, inequality, polinomial denotes expressions of the (formal) theory, and thus they belongs to the meta-theory.

I think that when he speaks of "logic", he means the (formal) theories of pure logic : the sentential calculus and the predicate calculus.
In this sense, they are formal theory with their own "domain of discourse" : sentences (or propositions) for the sentential calculus.
In the same way as for (formal) arithmetic, the concept e.g. of tautology does not belong to the (logic) calculus but to the meta-theory regarding the sentential calculus, i.e. to meta-logic.
