diff --git a/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h b/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h
index e9e082df793..24cb74fa0e4 100644
--- a/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h
+++ b/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h
@@ -2158,12 +2158,12 @@ private: //------------------------------------------------------- private data
   }
 
 #if !defined(CGAL_CFG_NO_CPP0X_RVALUE_REFERENCE) && !defined(CGAL_CFG_NO_CPP0X_VARIADIC_TEMPLATES)
+
+  /// \relates Surface_mesh
+  /// Inserts the surface mesh in an output stream in PLY format.
+  /// All vertex and face properties with simple types are inserted in the stream.
   template <typename P>
-#ifdef DOXYGEN_RUNNING
-  bool write_ply(std::ostream& os, const Surface_mesh<P>& sm)
-#else
-  bool write_ply(std::ostream& os, const Surface_mesh<P>& sm, std::string* comments = NULL)
-#endif
+  bool write_ply(std::ostream& os, const Surface_mesh<P>& sm, const std::string& comments = std::string())
   {
     typedef Surface_mesh<P> SMesh;
     typedef typename SMesh::Vertex_index VIndex;
@@ -2191,9 +2191,9 @@ private: //------------------------------------------------------- private data
        << ((get_mode(os) == IO::BINARY) ? "format binary_little_endian 1.0" : "format ascii 1.0") << std::endl
        << "comment Generated by the CGAL library" << std::endl;
 
-    if (comments != NULL)
+    if (comments != std::string())
     {
-      std::istringstream iss (*comments);
+      std::istringstream iss (comments);
       std::string line;
       while (getline(iss, line))
       {
@@ -2607,12 +2607,26 @@ private: //------------------------------------------------------- private data
   }
  
 #if !defined(CGAL_CFG_NO_CPP0X_RVALUE_REFERENCE) && !defined(CGAL_CFG_NO_CPP0X_VARIADIC_TEMPLATES)
+
+  /// \cond SKIP_IN_MANUAL
   template <typename P>
-#ifdef DOXYGEN_RUNNING
   bool read_ply(std::istream& is, Surface_mesh<P>& sm)
-#else
-  bool read_ply(std::istream& is, Surface_mesh<P>& sm, std::string* comments = NULL)
-#endif
+  {
+    std::string dummy;
+    return read_ply (is, sm, dummy);
+  }
+  /// \endcond
+
+  /// \relates Surface_mesh
+  /// Extracts the surface mesh from an input stream in Ascii or
+  /// Binary PLY format and appends it to the surface mesh `sm`.  The
+  /// operator reads all properties for vertices and faces found in
+  /// the PLY input.
+  /// \pre The data in the stream must represent a two-manifold. If this is not the case
+  ///      the `failbit` of `is` is set and the mesh cleared.
+
+  template <typename P>
+  bool read_ply(std::istream& is, Surface_mesh<P>& sm, std::string& comments)
   {
     if(!is)
     {
@@ -2629,8 +2643,7 @@ private: //------------------------------------------------------- private data
       return false;
     }
 
-    if (comments != NULL)
-      *comments = reader.comments();
+    comments = reader.comments();
 
     for (std::size_t i = 0; i < reader.number_of_elements(); ++ i)
     {