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: This study did not demonstrate a species difference regarding the role of the amines on the pineal in spite of the immature blood - brain barrier in the young chick and the intact barrier in the rat .
### Output Text:
This study did not demonstrate a species difference regarding the role of the <span class="chemical">amines</span> on the pineal in spite of the immature blood - brain barrier in the young chick and the intact barrier in the rat . 