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 hemorrhagic F2 pituitaries were all among the most massive , indicating that some of the genes regulate both phenotypes .
### Output Text:
The hemorrhagic F2 pituitaries were all among the most massive , indicating that some of the genes regulate both phenotypes . 