season replacement show. Since nothing needed replacing on their  schedule, the seriess premiere date was pushed back to Fall 1968  where it inevitably replaced Irwin Allens "Voyage" series on the  schedule. The 1967 start of the series filming helps explain the  difference in appearance of actor Stephen Arngrim from year one to  year two, because in actuality THREE years have transpired over the  course of the series 51 episodes!