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. 



