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: Interestingly , the size of the population appears to be correlated with the frequency of behavioral seizures , because animals with more ectopic granule cells in the hilus have more frequent behavioral seizures .
### Output Text:
Interestingly , the size of the population appears to be correlated with the frequency of behavioral seizures , because animals with more ectopic granule cells in the hilus have more frequent behavioral seizures . 