@SIR-GERMAN:
68-pin drives are so called Wide SCSI drives, compared to 50-pin drives which are Narrow SCSI drives. The difference is that the Wide SCSI drives have a 16-bits wide databus, while the Narrow SCSI drives have a 8-bit databus.
Like all I/O-signals on the SCSI-bus, the extra 8-bits on the Wide SCSI drives, usually called the upper Byte needs to be terminated.
So, if you attach a Wide SCSI drive (68-pin) to a Narrow SCSI bus (50-pin) using a 50->68pin adapter that doesn't terminate this upper Byte, it will in most likely cause the drive to to malfunction as those signals (the upper Byte)then will be in an undefined state (the drive doesnt know if they are ones or a zeroes).
Check
this page for more information.
/Patrik