Updated version
I just noticed that the filling for the bananas is done using different shades of gray:

The code:
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[>=latex]
\coordinate (A) at (0,0) ;
\coordinate (B) at (0,-5) ;
\coordinate (C) at (4,0) ;
\coordinate (D) at (4,-5) ;
\filldraw[top color=gray!20,bottom color=gray!70,middle color=gray!30]
% the banana to the left
(A) to[out=-110,in=110]
coordinate[pos=0.07] (auxlu)
coordinate[pos=0.93] (auxll)
(B) to[out=140,in=-140]
(A);
% the banana to the right
\filldraw[top color=gray!70,bottom color=gray!20,middle color=gray!30] (C) to[out=-70,in=70]
coordinate[pos=0.07] (auxru)
coordinate[pos=0.93] (auxrl)
(D) to[out=40,in=-40]
(C);
\draw[thick,looseness=1.3]
% the upper curve
(auxlu) to[bend right] (auxru)
% the lower curve
(auxll) to[bend left] (auxrl);
% the circle
\node[circle,draw=green!60!black,inner sep=0.5cm]
at (1.2,-2.5) (circle) {};
% the arrow
\draw[<->,thick]
(circle.south) -- ++(-45:3cm);
\end{tikzpicture}
\end{document}
Initial version
The code (with explanatory comments):
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[>=latex]
\coordinate (A) at (0,0) ;
\coordinate (B) at (0,-5) ;
\coordinate (C) at (4,0) ;
\coordinate (D) at (4,-5) ;
\filldraw[fill=gray!20]
% the banana to the left
(A) to[out=-100,in=100]
coordinate[pos=0.05] (auxlu)
coordinate[pos=0.95] (auxll)
(B) to[out=120,in=-120]
(A)
% the banana to the right
(C) to[out=-80,in=80]
coordinate[pos=0.05] (auxru)
coordinate[pos=0.95] (auxrl)
(D) to[out=60,in=-60]
(C);
% the upper curve
\draw
(auxlu) to[bend right] (auxru);
% the lower curve
\draw
(auxll) to[bend left] (auxrl);
% the circle
\node[circle,draw=green,inner sep=0.5cm]
at (1.8,-2.5) (circle) {};
% the arrow
\draw[<->]
(circle.south) -- ++(-45:3cm);
\end{tikzpicture}
\end{document}
Remarks
For the "banana" shaped figures, the out=
, in=
operations.
For the curved paths the bend
operation (the out=
, in=
operations could also have been used).
The bend cirves are drawn by joining some auxiliary coordinates placed upon the inner path for the "bananas" with the help of pos=
.
The circle is a \node
with circle
shape.
The arrow was drawn using the anchors for the node.