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 conclusion , the present study demonstrates gender differences in the development of the apomorphine - induced aggressive behavior and indicates that the female rats do not fill the validation criteria for use in this method .
### Output Text:
In conclusion , the present study demonstrates gender differences in the development of the <span class="chemical">apomorphine</span> - induced aggressive behavior and indicates that the female rats do not fill the validation criteria for use in this method . 