In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In male animals , repeated apomorphine treatment induced a gradual development of aggressive behavior as evidenced by the increased intensity of aggressiveness and shortened latency before the first attack toward the opponent .
### Output Text:
In male animals , repeated <span class="chemical">apomorphine</span> treatment induced a gradual development of aggressive behavior as evidenced by the increased intensity of aggressiveness and shortened latency before the first attack toward the opponent . 