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: Co - administration of nefiracetam and apomorphine during training or 10h thereafter produced no significant anti - amnesic effect .
### Output Text:
Co - administration of <span class="chemical">nefiracetam</span> and <span class="chemical">apomorphine</span> during training or 10h thereafter produced no significant anti - amnesic effect . 