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: Instead , numerous abnormal vesicles containing one or several dark granules were observed in the cytoplasm of cells from all the epithelial layers .
### Output Text:
Instead , numerous abnormal vesicles containing one or several dark granules were observed in the cytoplasm of cells from all the epithelial layers . 