TFDMemtable FieldDefs does not consider lookup fields?

Question

Using Delphi 10.2.3, I dropped in a form a Firedac TFDMemTable component which was I used Field Editor to define 5 fields, one of those fields is a Lookup Field (FieldKind = fkLookup) .

I created a code to scan all fields of the MemSource MemTable to add those fields in a MemDestination Memtable.

I had a problem in scan the MemSource.FieldDefs because its total number of fields did not consider the Lookup one ! See the code :

    procedure TFormA.BTCopyFieldsClick(Sender: TObject);
    var
       i         : integer;
    begin

      for I := 0 to MemSource.FieldDefs.Count-1 do
      begin
            if (memSource.Fields.Fields[i].FieldKind = FkData) then
                memDestination.FieldDefs.Add (
                         memSource.FieldDefs.Items[i].DisplayName,
                         memSource.FieldDefs.Items[i].DataType,
                         memSource.FieldDefs.Items[i].Size,
                         memSource.FieldDefs.Items[i].Required
                         )
           Else

                ShowMessage( GetEnumName(TypeInfo(TFieldKind),
                             Integer(memSource.FieldDefs.Items[i].Datatype)
                           );

           memDestination.CreateDataSet;
           memDestination.CopyDataSet(memSource,[coRestart, coAppend]);
      end;
   end;

I realized that memSource.FieldDefs.Count had 4 fields only, it missed the 5th one which was a lookup type .

However memSource.Fields.Count accounts for 5 fields, that is correct.

The questions are :

1. Is lookup field defined at design time considered in FieldDefs ?
   (if it is not considered, so WHY ?)

2. Why memSource.FieldDefs.Count is different from memSource.Fields.Count ? (i.e. I have more fields in the memtable than in its definition )

Am I doing somethinf wrong in the above code ? What ?

Thanks in advance !!