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Terms and definitions for Chapter A2


the main bone, made up of many small bones joined together, that runs along the middle of the back in some animals


a hard outer covering that supports and protects some animals without backbones


to shed an animal's outer covering


organs for breathing found in fish and amphibians


one of a large group of animals with backbones that live part of their lives in water and part on land


an animal with a backbone that has dry, scaly skin


an animal with a backbone that usually has hair on its body and feeds milk to its young


a simple, automatic behavior


the cause of a behavior


a behavior caused by a stimulus

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