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 , scopolamine and ritanserin co - administration resulted in a significant decrease in escape latencies and traveled distances as compared to the scopolamine - treated rats .
### Output Text:
However , <span class="chemical">scopolamine</span> and <span class="chemical">ritanserin</span> co - administration resulted in a significant decrease in escape latencies and traveled distances as compared to the <span class="chemical">scopolamine</span> - treated rats . 