\begin{tikzpicture}
                  \tikzset{
                    arrowMe/.style={postaction=decorate,
                      decoration={markings, mark=at position .55 with {\arrow[very thick]{#1}}
                      } }}
                    \draw[arrowMe=stealth](0,0)--node[below]{\(a\)}(5,0);
                    \draw[arrowMe=stealth](0,3)--node[left]{\(b\)}(0,0);
                    \draw[arrowMe=stealth](0,3)--node[above]{\(a\)}(5,3);
                    \draw[arrowMe=stealth](5,0)--node[right]{\(b\)}(5,3);
                    \draw[dashed](0,1.25)--(5,1.25);
                    \draw[dashed] (0,1.75)--(5,1.75);
                      \begin{scope}[xshift=2.5cm,yshift=2cm]
                        \draw (0,0) rectangle (.4,.4);
                        \draw (.4,.05) to [bend left=20] (.2,.15);
                        \fill[color=black](.4,.3) to [bend left=40] (.3,.4) to (.4,.4) to (.4,.3);
                      \end{scope}
                      \begin{scope}[xshift=2cm,yshift=2cm]
                        \draw (0,0) rectangle (.4,.4);
                        \draw (0,.05) to [bend right=20] (.2,.15);
                        \fill[color=black](0,.3) to [bend right=40] (.1,.4) to (0,.4) to (0,.3);
                      \end{scope}
                      \begin{scope}[xshift=3.8cm,yshift=2.3cm]
                        \draw (0,0) rectangle (.4,.4);
                        \draw (.4,.05) to [bend left=20] (.2,.15);
                        \fill[color=black](.4,.3) to [bend left=40] (.3,.4) to (.4,.4) to (.4,.3);
                      \end{scope}
                        \draw (5,2.3)--(4.8,2.3)--(4.8,2.7)--(5,2.7);
                        \draw (0,.3)--(.2,.3)--(.2,.7)--(0,.7);
                        \fill[color=black](.1,.3) to [bend left=40] (.2,.4) to (.2,.3) to (.1,.3);
                        \draw (.2,.65) to [bend right=20] (0,.55);
                      \begin{scope}[rotate around={240:(1.2,1.2)}]
                      \begin{scope}[xshift=1cm,yshift=1cm]
                        \draw (0,0) rectangle (.4,.4);
                        \draw (0,.05) to [bend right=20] (.2,.15);
                        \fill[color=black](0,.3) to [bend right=40] (.1,.4) to (0,.4) to (0,.3);
                      \end{scope}
                      \end{scope}
                      \draw[thick,->] (.3,.5)--+(.6,.5);
                      \draw[thick,->] (1.5,1.4)--+(.4,.5);
                      \draw[thick,->] (3,2.2)--+(.6,.2);
                      \draw[thick,->] (4.3,2.5)--+(.4,0);
\end{tikzpicture}