Abstract
Summary
1. Alexandrines or roof rats (Rattus rattus) have shorter small intestines and longer large intestines than do Norway rats (Rattus norvegicus). 2. The intestines of Norway rats have about twice as many Peyer's patches on the average as do those of Alexandrine rats, averaging 16-19 as compared to 9. 3. The intestines of domestic Norway rats have more Peyer's patches than do those of wild Norways. 4. Peyer's patches first become visible when the rats reach an age of 15 days. The number does not appear to change with age.
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