Final answer:
Heathcliff puts a lock of his own hair in Catherine's locket alongside Edgar's hair in Chapter 16 of 'Wuthering Heights', symbolizing his enduring love and connection to her.
Step-by-step explanation:
In Chapter 16 of Wuthering Heights, Heathcliff places a lock of his own hair into Catherine's locket that she wears on her deathbed. This locket originally contains a lock of Edgar's hair, but Heathcliff replaces it with his own, intertwining it with Edgar's to ensure that both are kept together. This act highlights the intense and complex relationship that Heathcliff has with Catherine, indicative of his deep love and desire to be connected with her even after death.