The effects of dietary nitrogen levels in relation to ammonotelism, cation excretion and water requirements were examined in the American cockroach, Periplaneta americana (L.). Very little ammonia is released from the respiratory surfaces; rather it appears to be eliminated in the faeces, presumably as ammonium ions. Microflora present in the hindgut may contribute significantly to the production of excreted ammonia under certain dietary conditions. Injections of buffers containing either NH4+, K+ or Na+ resulted in normal (NH4+ and K+), or less than normal (Na+) levels of ammonia excretion. Faeces collected from cockroaches maintained on twelve different diets containing various levels and sources of nitrogen were examined for NH4+, K+, Na+, Ca2+ and Mg2+. Ammonium ions were found to be the major cations contained in the faeces and were excreted in increasing amounts as the dietary nitrogen levels increased. The ad libitum water requirements were closely correlated with dietary nitrogen levels, and subsequently with ammonia excretion. Certain aspects concerning the possible factors involved, and the significance of ammonia excretion, are discussed.

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