\begin{tikzpicture}
% help guide lines
%\draw[help lines] (0,0) grid [step = 5 mm](10,10);
%\foreach \x in {0,1,...,10}
%   \draw [help lines] (\x,0) node [below,%
%          font=\footnotesize] {$\x$} -- (\x,0);
%\foreach \y in {0,1,...,10}
%   \draw [help lines] (0,\y) node [left,%
%          font=\footnotesize] {$\y$} -- (0,\y);
%
% define model box
\newcommand{\modelbox}[2]{
	% input arrow  
	\coordinate (startarrow) at ({#1},{#2});
	\coordinate	(endarrow) at ($(startarrow)+(2.5,0)$);
	\draw [-stealth]($(startarrow) + (0,1 * 1)$) -- ($(endarrow)+(0,1* 1)$) node[above, midway] {$f(t)$};
	\draw [-stealth]($(startarrow) + (0,1 * 0)$) -- ($(endarrow)+(0,1* 0)$) node[above, midway, xshift=-0.65mm] {$\vec{x}_{0} \,, \dot{\vec{x}}_{0}$};
	% box
	% left low corner
	\coordinate (llcorner) at (2.5,-0.5);
	% right up corner
	\coordinate (rupcorner) at(6.5,1.5);
	\draw (llcorner) rectangle (rupcorner) node [midway]{dynamic system};
	% output arrow
	\coordinate (outputstartarrow) at (6.5,0.5);
	\coordinate	(outputendarrow) at (8.5,0.5);
	\draw [-stealth](outputstartarrow) -- (outputendarrow) node[above, midway] {$\vec{x}(t)$};
};
% 1 - plot the system model
\begin{scope}[yshift = 60mm]
   \modelbox{0}{0};  
\end{scope}
% 2 - plot second model and connection
\begin{scope}[yshift = 25mm]
   \modelbox{0}{0};
   \fill (1.75,1) circle (1.4pt);
   \fill (1,0) circle (1.4pt);
\end{scope}
% connect system model
   \draw (1.75,1) -- (1.75,3.5);
   \draw (1,2.5) -- (1,0);
% box model
\begin{scope}[xshift = 0mm]
   % input arrow  
	\coordinate (startarrow) at (1.75,1);
	\coordinate	(endarrow) at (2.5,1);
	\draw [-stealth](startarrow) -- (endarrow) node[below, midway] {$f(t)$};
	\draw [-stealth](1,0) -- (2.5,0) node[below, midway] {$\vec{x}_{0} \,, \dot{\vec{x}}_{0}$};
	% box
	% left low corner
	\coordinate (llcorner) at (2.5,-0.5);
	% right up corner
	\coordinate (rupcorner) at(6.5,1.5);
	\draw (llcorner) rectangle (rupcorner) node [midway]{model $\theta$};
	% output arrow
	\coordinate (outputstartarrow) at (6.5,0.5);
	\coordinate	(outputendarrow) at (8.5,0.5);
	\draw [-stealth](outputstartarrow) -- (outputendarrow) node[above, midway] {$\vec{x}(t)$};
\end{scope}
\end{tikzpicture}