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Figure 10PARADOXICAL SLEEP among three vertebrate classes of increasing evolutionary complexity is shown as a percentage of each animal's time spent in light sleep. None is known in the case of the reptile, a tortoise; in the case of the hen it is only two-tenths of 1 percent of the total. In the case of each of the four mammal species shown, the newborn spend at least twice as much time in paradoxical sleep (color) as do their adult counterparts (black). |