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: The fetal kidneys in the PCE group displayed an enlarged Bowman ' s space and a shrunken glomerular tuft , accompanied by a reduced cortex width and an increase in the nephrogenic zone / cortical zone ratio .
### Output Text:
The fetal kidneys in the PCE group displayed an enlarged Bowman ' s space and a shrunken glomerular tuft , accompanied by a reduced cortex width and an increase in the nephrogenic zone / cortical zone ratio . 