Both are yaoi manga that involve a scientist doing kinky sexual experiments to the uke. Both have fetishy sex scenes (involving machines and robot dogs in Gingaku Hakase to Marmot, and involving tentacle plants in Hakase to Neko). However, Gingaku Hakase to Marmot has a decent plot and even some world development, while Hakase to Neko is pretty much pure yaoi smut. Gingaku Hakase to Marmot is definately the better of the two, but if you like kinky, fetish-filled yaoi then you should check out both.
Both of these are shounen-ai one shots that feel similar to me. They both involve an older man with a fetish, and are fairly good. Fans of one would probably enjoy the other as well.