Comparison of Intestinal Lengths and Peyer's Patches in Wild and Domestic Norway and Wild Alexandrine Rats.

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