\documentclass{standalone}
\input{common-headers}
\input{sigles}
\begin{document}
\begin{tikzpicture}[node distance=4cm,
  normalNodes/.style={inner sep=10pt,outer sep=2pt,minimum width=2.5cm},
  main/.style={normalNodes,draw=black},
  high/.style={normalNodes,draw=black,fill=black!20},
  low/.style= {normalNodes,draw=black,fill=black!40},
  regTo/.style={-Stealth,thick},
  mainTo/.style={-Stealth,thick}]
  \node (Main)        [main] {\texttt{Main}};
  \node (Morphogen)   [high,below of=Main, xshift=-2cm] {\texttt{Morphogen}};
  \node (Bacterium)   [high,left of=Morphogen]  {\texttt{Bacterium}};
  \node (Zone)        [high,right of=Morphogen] {\texttt{Zone}};
  \node (Coupling)    [high,right of=Zone]      {\texttt{Coupling}};
  \node (BoundingBox) [low,below of=Zone]       {\texttt{BoundingBox}};
  \node (OpenCL)      [low,below of=Coupling]   {\texttt{OpenCL}};
  \node (SBGP)        [low,right of=OpenCL]     {\texttt{SBGP}};
  \node (Packfile)    [low,below of=Morphogen]  {\texttt{Packfile}};
  \node (Viewer)      [low,below of=Bacterium]  {\texttt{Viewer}};
  
  \coordinate (MZ) %
  at (barycentric cs:Morphogen=1,Zone=1) {};
  \draw [mainTo] (Main) to [out=-90,in=90] (Bacterium);
  \draw [mainTo] (Main) to [out=-90,in=90] (Morphogen);
  \draw [mainTo] (Main) to [out=-90,in=90] (Zone);
  \draw [mainTo] (Main) to [out=-90,in=90] (Coupling);
  \draw [mainTo] (Main) to [out=-90,in=120] (BoundingBox);
  \draw [mainTo] (Main) to [out=0,in=90]   (SBGP);
  \draw [mainTo] (Main) to [out=-90,in=90] (MZ) to [out=-90,in=45] (Viewer);

  \node (BM) [inner sep=1pt, fill=black, draw=black, yshift=-10pt, circle]%
  at (barycentric cs:Morphogen=1,Bacterium=1) {};
  \draw [thick] (Bacterium) to [out=0,in=135] (BM);
  \draw [thick] (Morphogen) to [out=180,in=45] (BM);
  \draw [regTo] (BM) to [out=-90,in=90] (Viewer);
  \draw [regTo] (BM) to [out=-85,in=90] (Packfile);
  \draw [regTo] (BM) to [out=-70,in=145] (BoundingBox);
  \draw [regTo] (BM) to [out=-55,in=155] (OpenCL);

  \draw [regTo] (Zone)      to  (BoundingBox);
  \draw [regTo] (Zone)      to  [out=-70,in=135] (OpenCL);
  \draw [regTo] (Coupling)  to  (OpenCL);
  \draw [regTo] (Coupling)  to  [out=-70,in=135] (SBGP);
%

\end{tikzpicture}
\end{document}