Peanuts by Charles Schulz for May 05, 1965
Transcript:
Snoopy lies on his doghouse and thinks, "I wonder what happened to all my brothers and sisters . . ."<BR><BR> Snoopy thinks, "We used to have a pretty good time there at the ol' 'Daisy Hill Puppy Farm.'"<BR><BR> Snoopy thinks, "Maybe I can get in touch with them . . ."<BR><BR> Snoopy watches as Charlie Brown prepares to write a letter. Charlie Brown says, "I never thought I'd end up being a male secretary to a beagle!"<BR><BR>
So much for the “only dog” strip of 1959. But this makes more sense, dogs are born in litters with multiple puppies.