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: The saline - and apigenin - treated rats that did not step through into the dark compartment during the cut - off time ( 540 s ) were retested weekly for up to eight weeks .
### Output Text:
The saline - and <span class="chemical">apigenin</span> - treated rats that did not step through into the dark compartment during the cut - off time ( 540 s ) were retested weekly for up to eight weeks . 