Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 334 ELEMENTARY BIOLOGY animals we find that much more is suppHed for the young. The lobster and crayfish mothers carry the eggs about on their abdominal legs, or swimmerets, and even the young em- bryos until they are able to care for themselves. Among the insects there are some that abandon their eggs as soon as laid, whereas others provide shelter and food for the young. Most fish leave their eggs in the water with- out further attention. There are a few fishes
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 334 ELEMENTARY BIOLOGY animals we find that much more is suppHed for the young. The lobster and crayfish mothers carry the eggs about on their abdominal legs, or swimmerets, and even the young em- bryos until they are able to care for themselves. Among the insects there are some that abandon their eggs as soon as laid, whereas others provide shelter and food for the young. Most fish leave their eggs in the water with- out further attention. There are a few fishes, like the stickleback, that prepare a rather rough protection, or nest, for the eggs (Fig. 157). Some toads carry their eggs about in the mouth until they are hatched. Among the reptiles and birds the egg begins its development inside the parent's body, and receives a large amount of food and a protective covering. Most reptiles and some birds leave their eggs to be hatched by the heat of the sun, or at ordinary temperatures. Most of the common birds, however, build more or less elabo- rate nests and care for the fledglings and for the eggs, besides supplying heat for the hatching. The feeding of the young birds by the parents is a very interesting operation to obser\^e, and it shows a very complex development of instincts. 388. Infancy among mammals. When we come to the mammals, the dependence of the young upon the parents is carried even farther. Not only does the egg develop inside the body of the mother until it has acquired the general form characteristic of the species, but it is nourished by the parent Fig. 158. Wallaby and young The babies are not only protected and kept warm in the njarsitpbim, or pouch, but are also nourished by a milky secretion produced by glands in the lining of the pouch
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