It only has a hole on the top.
I think it is a different model with a hole on bottom.

Anyway the basic concept of a humidity chamber is a closed space filled with damp moss with a hole for the reptile to enter.

Most reptiles know how to take care of themselves - problems like bad sheds are usually the result of us not providing them with what they need to do so.

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I can't say for sure - but the difference between young alligator lizards and adults as far as needing a humidity chamber - young ones are smaller and thus more likely to be eaten by an aquatic predator such as a trout or a bird, so they may instinctively be less willing to soak themselves for long periods of time.

Also - I use coconut fiber for my adults, and they have a burrow dug under the water dish - that may act as a humidity source for them. I'm using wood chips for the babies because they are too difficult to locate when they burry themselves in coconut fiber.
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3.6 L. getula californiae - 16 eggs (Cal. King)
1.1 L. getula nigrita (MBK)
1.0 Pantherophis guttatus guttatus (Corn)
0.1 Pituophis catenifer catenifer (Pacific gopher)
3.3 Elgaria multicarinata multicarinata - 14 eggs (Cal. Alligator Lizard)