The Norway Rat (Rattus norvegicus)

Rattus norvegicus adult males range in weight from 450 to 520 grams. In contrast, at between 250 and 300 grams, the females of the species are somewhat smaller (2:49). The animal's coat is typically brown, although mink, pearl, and albino mutants do exist. The mink rat is a light brown with a variable light or white undercolor; the pearl rat is white with dark brown pigment in the tips of its hairs (7:142).

The zoological nomenclature for the Norway rat was devised in 1924. The scientist, H. H. Donaldson, named the species (6:1-6). Like other mammals, R. norvegicus belongs to the animal kingdom, the Phylum Chordata, and the Class Mammalia. Furthermore, the Linnean system of taxonomic classification also places the species in the Suborder Rodentia and the Family Muridae (8:121, 135, 209).

The history of the Norway rat can be traced back to the eighteenth century. The animal has no obvious connection to Norway. However, it is widely believed that the organism originated in the temperate regions of central Asia (2:47-54). More specifically, the species may have evolved in the "wild country between the Caspian Sea and Tobolsk (6:1-6)."

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may bear between 7 and 10 litters. For the most part, litter size decreases and litter interval increases with the approach of sexual senescence. The female rat is usually ready to mate again only 2 to 4 days postweaning (2:47-54). The Norway rat is an omnivorous animal. Natural selection has endowed it with a truly remarkable gnawing apparatus. Like other murine rodents, its dental formula is 1/1 incisors and 3/3 molars. The incisors, however, act as chisels. Moreover, the teeth erupt continuously. Furthermore, the rat's cheeks close into a long diastema separating the incisors from the oral cavity. Such anatomic features--in addition to powerful jaw muscles--only enhance the organism's gnawing capabilities (2:47-54). In fact, it is rumored that rats can even gnaw through concrete. Norway rats are usually nocturnal. In addition, they are cautious feeders. A new food or a food that is in a strange location may elicit an avoidance response (1:86). Olfactory stimuli are important determinants of what a rat will and will not eat (5:446). Various researchers have determined that many patterns of behavior are socially transmitted. For example, certain olfactory cues may attract rats to food sites. These cues could inv
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Some common words found in the essay are:
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Approximate Word count = 1511
Approximate Pages = 6 (250 words per page)