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: Differential effects of gamma - hexachlorocyclohexane ( lindane ) on pharmacologically - induced seizures .
### Output Text:
Differential effects of <span class="chemical">gamma - hexachlorocyclohexane</span> ( <span class="chemical">lindane</span> ) on pharmacologically - induced seizures . 