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: Experiments with N - and C - terminal fragments revealed that the C - terminal tetrapeptide ( CCK - 5 - 8 ) was the active centre of the CCK octapeptide molecule .
### Output Text:
Experiments with N - and C - terminal fragments revealed that the C - terminal tetrapeptide ( CCK - 5 - 8 ) was the active centre of the CCK octapeptide molecule . 