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: However , ciprofloxacin - and norfloxacin - treated rats did not differ significantly from each other in various behavioural parameters .
### Output Text:
However , <span class="chemical">ciprofloxacin</span> - and <span class="chemical">norfloxacin</span> - treated rats did not differ significantly from each other in various behavioural parameters . 