Dancing and courting
At a ball, single people have an opportunity to mingle, which is what the dance represents. Just like in animal mating rituals, humans also dance to attract mates, but the dance is a little different. One sees the way social niceties apply in that formal setting, so personalities are on full display. The scandalous people make scandals. The dancers go dancing. This represents the question of the novel: Will Tarr ever settle down with a mate, or is he just at the dance to have fun?
The duel
Another element of human romance is exposed in this book, the issue of male competition. The competitive nature of talking with single women and trying to attract them, while other men are around doing the same thing—it can lead to violence. The duel symbolizes the competitive nature of romance, because multiple people want the same person, and romance brings out the most aggressive parts of some people.
The motif of food and sex
There is constant innuendo throughout the novel pertaining to food. When they finally are eating oysters, we learn why this is such a consistent idea: both food and sex involve physical pleasure, and they both are animal instinct, so when the men eating in a suggestive way, they are borrowing from the erotic aspect of eating and being 'satisfied.'
Rose and Prism
Although the novel ends in a situation much like it began, the last two women who Tarr dates simultaneously (he does it all the time it seems) are Rose and Prism whose very names are symbolic, especially since they are static characters who don't even get mentioned until the end of the novel. They represent his core problem—instead of seeing the world in all its emotional color (like a prism rainbow), he prefers the rose-colored world of temporary satisfaction.
Bertha
Because of the strange conflicts that exist within Tarr, Bertha ends up symbolizing some unspoken agreement Tarr has with himself. He is constantly judging Bertha as if she represents the universe's divine punishment against him, and then he guilts himself into still marrying her—but that's exactly why Bertha represents reason and order, because Tarr is not unacceptable to her except that he will not commit and take responsibility for himself. So, Bertha represents responsibility, specifically she represents Tarr's aversion to responsibility.
