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A distinguishing feature of rodents, including rats, is the absence of canines and the
presence of prominent incisors. Rats are monophydontic, meaning they grow one set
of teeth in their lifetime. The enamel of the rodent incisor contains iron, which gives
it its yellow-orange color. Rats are mammals and as such, possess many similarities
with other mammals. Only the peculiarities of the rat’s anatomy are addressed. Male
rats reach puberty at 40 - 60 days of age. Descent of the testes usually occurs
between days 30 - 60. Sperm counts vary by strain. The male rat has an os penis.
Male rats have the following accessory sexual organs: ampulla, seminal vesicles,
prostate, bulbourethral glands, coagulating glands, and preputial glands. The
coagulating gland and prostatic and vesicular secretions are responsible for the
copulation plug, a firm plug deposited in the vagina of the female after copulation.
(This plug, when found outside the female rat, is capsuleshaped and approximately
5 mm long.) The male rat has no nipples. The adult male rat has a prominent
scrotum and a longer anogenital distance than the female rat.