Gudrun and Ursula were co-mates. The second child, with her long, sleepy body and her endless chain of fancies, would have nothing to do with realities. She was not for them, she was for her own fancies. Ursula was the one for realities. So Gudrun left all such to her elder sister, and trusted in her implicitly, indifferently. Ursula had a great tenderness for her co-mate sister. When the author calls the two girls "co-mates," what does he mean?