. A manual of zoology. Zoology. 55S CHORDATA others viviparous, 1)Ut are distinguished Ijy the duration of pregnancy. The eggs of the ^•iviparous s])ecies are so small (about .01 inch) that they have a total, nearly equal segmentation. Such eggs require nourishment from the mother in order to produce an animal with the complicated structure of a mammal. Since in the Didelphia the uterine nourishment is usually very incomplete, the period of pregnancy is very short, in com- parison with the Monodelphia, in which a placenta, a complicated apparatus for the nourishment of the young, appears; henc
. A manual of zoology. Zoology. 55S CHORDATA others viviparous, 1)Ut are distinguished Ijy the duration of pregnancy. The eggs of the ^•iviparous s])ecies are so small (about .01 inch) that they have a total, nearly equal segmentation. Such eggs require nourishment from the mother in order to produce an animal with the complicated structure of a mammal. Since in the Didelphia the uterine nourishment is usually very incomplete, the period of pregnancy is very short, in com- parison with the Monodelphia, in which a placenta, a complicated apparatus for the nourishment of the young, appears; hence the marsupials, with their small imperfectly formed young, are of en called Aplacentalia; the JMonodelplua, Placentalia. All mammals care for the voung, this being chiefly or wholly done by the mother, who not only supplies them with milk but protects them in nests. Most mammals are monogamous, some j)olygamous, while in others there is no permanent association of the The body temperature is constant and ranges from 36° to 41° C. (98° to 106° F.); in Echidna it is only 26° to 34° C. (79° to 83° F.). In most, continual feeding is necessary for existence; from this rule there are a few exceptions, like the bears, marmots, badgers, etc., which hibernate during the winter, taking no food. .At this time there is a fall in the temperature (in the marmots nearly to freezing) due to the diminished metabolism. Sub Class I. Monoirentata {Oniilhodelphia, Prototlicria). A few mammals, confined to Australia and New Guinea, are the only living representatives of the group. They are distinguished from all other mammals by laying eggs about half an inch long, rich in yolk and with soft shells. These undergo in the uterus a discoidal (meroblastic) segmentation and are then incubated by Omillwrli vn- clnis in a nest, by Echidna in a temporary pouch (marsupium) on the ventral sur- face of the body. On hatcliing the young are nourished by the secretion of j^ enormously enlarged
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
