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: Neurotoxicity was assessed for behavioral ( tail - flick test ) , neurophysiological ( nerve conduction velocity in the tail nerve ) , morphological , morphometrical and analytical effects .
### Output Text:
Neurotoxicity was assessed for behavioral ( tail - flick test ) , neurophysiological ( nerve conduction velocity in the tail nerve ) , morphological , morphometrical and analytical effects . 