I need to calculate $\int \dfrac{dx}{\sqrt{1-x^4}}$. I know that: $\int \dfrac{dx}{\sqrt{1-x^2}} = \arcsin{x} + \text{const}$.

But why then $\int \dfrac{dx}{\sqrt{1-x^4}} \ne \arcsin{x^2} + \text{const}$ ?

And how can it be calculated?