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: METHODS : Pregnant rats were treated with fluoxetine ( 10 mg / kg ) from Day 11 through Day 21 of gestation .
### Output Text:
METHODS : Pregnant rats were treated with <span class="chemical">fluoxetine</span> ( 10 mg / kg ) from Day 11 through Day 21 of gestation . 