Dealing with organic compounds, it is metamerism that deserves chief attention, as it has largely developed our notions as to molecular structure.
These laws have the advantage of being applicable to the mutual transformations of isomers, whatever be the nature of the deeper origin, and so bring polymerism, metamerism and polymorphism together.
Bateson broke completely with the Dohrn-Semper view that the metamerism of Articulates and Vertebrates must be put down to inheritance from a common ancestor.
He held that metamerism was merely a special manifestation of the general property of repetition, common to all living things (cf.
In the articulates the metamerism is chiefly external--an articulation of the body wall.
The articulation or metamerism itself is not visible externally in the vertebrates; it is only seen in the muscular system when the non-articulated skin has been removed.
All three groups agree in the essential features of their organization, especially in the external articulation or metamerism of the long bilateral body, and also in the repetition of the internal organs in each joint or segment.
As this internal articulation or metamerism is mainly found in the vertebral column and the surrounding muscles, the sections or metamera were formerly called pro-vertebrae.
The internal articulation of the vertebrates is just as profoundly different from the external metamerism of the articulates as are their skeletal structure, nervous system, vascular system, and so on.
The Chaetopoda are characterized by a spacious coelom, which is divided into a series of chambers in accordance with the general metamerism of the body.
In the Oligochaeta there is a closer correspondence between external metamerismand the divisions of the coelom than is apparent in some Chaetopods.
The setae are implanted metamerically in accordance with the metamerism of the body, which consists of a prostomium followed by a number of segments.
The most remarkable feature presented by the heart of Nautilus is the possession of four instead of two auricles, a feature which is simply related to the metamerism of the branchiae.
In Chiton the renal organs are not affected by the metamerism as they are in Nautilus.
The only other example which we have of this metamerism in the Mollusca is presented by the Chitons.
There we find not two pairs of ctenidia merely, but sixteen pairs (in some species more) accompanied by a similar metamerism of the dorsal integument, which carries eight shells.
