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: Prospective study of the long - term effects of somatostatin analog ( octreotide ) on gallbladder function and gallstone formation in Chinese acromegalic patients .
### Output Text:
Prospective study of the long - term effects of somatostatin analog ( <span class="chemical">octreotide</span> ) on gallbladder function and gallstone formation in Chinese acromegalic patients . 