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: Neuroprotective effects of melatonin upon the offspring cerebellar cortex in the rat model of BCNU - induced cortical dysplasia .
### Output Text:
Neuroprotective effects of <span class="chemical">melatonin</span> upon the offspring cerebellar cortex in the rat model of <span class="chemical">BCNU</span> - induced cortical dysplasia . 