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: Lindane ( gamma - hexachlorocyclohexane ) is an organochlorine insecticide with known neurotoxic effects .
### Output Text:
<span class="chemical">Lindane</span> ( <span class="chemical">gamma - hexachlorocyclohexane</span> ) is an organochlorine insecticide with known neurotoxic effects . 