What did Tom's mistress buy for the apartment?

Tom's mistress, Myrtle, buys a puppy on the way to the apartment..... or shall we say, Tom buys it for her.

The airedale--undoubtedly there was an airedale concerned in it somewhere though its feet were startlingly white--changed hands and settled down into Mrs. Wilson's lap, where she fondled the weather-proof coat with rapture.

"Is it a boy or a girl?" she asked delicately.

"That dog? That dog's a boy."

"It's a bitch," said Tom decisively. "Here's your money. Go and buy ten more dogs with it."