U.S. Pat.  No.  6,851,402 discloses a two-stroke engine, the transfer channels of which are guided parallel to the cylinder longitudinal axis in the cylinder.  U.S. Pat.  No.  9,175,598 shows a two-stroke engine in which the transfer channels are guided helically around the cylinder bore and lead into the crankcase interior under the inlet opening and/or under the outlet opening.  A section of the transfer channels which connects the passage opening of the transfer channel at the cylinder flange to the mouth opening into the crankcase is guided in the crankcase.  On account of the different arrangement of the passage openings at the cylinder connecting flange, crankcases of different configurations are required for cylinders having straight transfer channels and for cylinders having transfer channels that extend helically around the cylinder bore.