In Morita's Geometry of Differential Forms p. 14 after the definition of atlas, he makes the following remark ($M$ is a manifold, $\{(U_\alpha,\varphi_\alpha)\}$ is an atlas of $M$, $V_\alpha$ are the images of $\varphi_\alpha$ in $\mathbb R^n$)
We remark that even if we cut off from $\mathbb R^n$ the part $V_\alpha$ used to make $M$, $\mathbb R^n$ fills the gap soon and is again complete, so that if the next part $V_\beta$ intersects “the imaginary hole”, $V_\beta$ can be taken out with complete shape. $\mathbb R^n$ is, so to speak, a “fountain” from which the parts of manifolds spring.
I understand the defintion of atlas but I don't understand what he is trying to explain here. What does he mean by "$\mathbb R^n$ fills the gap"?