CHAPTER VI.

HOMOLOGIES OF THE ARTICULATE SKELETON.

_Illustrations from this type_--Plan of structure entirely different--General plan of structure explained and modifications shown--Shrimp--Modification of segments and of appendages for various purposes: swimming, walking, eating, sense--Illustrated by other crustaceans--By myriapods-- By marine worms--Crabs--Embryonic development of crabs-- insects--Modification of segments and appendages--Mouth parts of insects 132

_Illustration of the law of differentiation_--Cells--Segments --Individuals--Homologies in other departments of animals, but these are less familiar--Between primary groups, homology untraceable in adult forms--But these also probably connected by common origin--Different views as to origin of vertebrates 144