What he wrote was essentially common knowledge at the time, not a novel theory that needed defending. That’s why elsewhere in this thread it is pointed out that you can’t judge it by today’s standards. We have different common knowledge today that people use as justifications for their opinions without feeling any need to cite a paper. Some of that knowledge is right and some wrong.

For a modern example, you could take a look at a comment that says his conclusions were wrong without citing any evidence.