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 purpose of this study was to evaluate and compare the effects of coniine and nicotine in the developing chick .
### Output Text:
The purpose of this study was to evaluate and compare the effects of <span class="chemical">coniine</span> and <span class="chemical">nicotine</span> in the developing chick . 