Elements of biology, with special Elements of biology, with special reference to their rôle in the lives of animals elementsofbiolog00buch Year: 1933 MULTICELLULAR ANIMALS 141 derived from the same embryonic structures, are homologous (Fig. 85). Homologies furnish the basis of anatomical studies and are indications of relationships between groups. In fact, the entire sci- ence of Comparative Anatomy is a study of homologies. In meta- FiG. 85.—Bones of the forclimb of a bird (left) and of a cat (right). In the bird the carpals are reduced to two, the others being fused with the metacarpals.
Elements of biology, with special Elements of biology, with special reference to their rôle in the lives of animals elementsofbiolog00buch Year: 1933 MULTICELLULAR ANIMALS 141 derived from the same embryonic structures, are homologous (Fig. 85). Homologies furnish the basis of anatomical studies and are indications of relationships between groups. In fact, the entire sci- ence of Comparative Anatomy is a study of homologies. In meta- FiG. 85.—Bones of the forclimb of a bird (left) and of a cat (right). In the bird the carpals are reduced to two, the others being fused with the metacarpals. It will also be noted that the metacarpals and phalanges in the bird are reduced in number, but that in all regions of the limbs the bones of the two animals are comparable. meric, or segmental animals, the parts of one appendage may be homologized with those of an appendage on another segment, as the parts of the maxillary appendage of a lobster are homologous with the parts of a walking leg (Fig. 86). In other words, within the same animal, particularly among segmented animals, homolo- gies between segmental organs occur serially as well as homologies with structures found in other groups of animals.
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