Colouration in Animals and Plants

by Alfred Tylor

As colouration, according to the views here set forth, depends upon structure, we may classify the Invertebrata thus:—

Protozoa			Structureless.
Cœlenterata Annuloida		Radiata.	Radiate structure.
Annulosa			Segmented "
Mollusca			Marginate "

The mollusca are said to be marginate in structure because, in those possessing shells—the mollusca proper—the shell is formed by successive additions to the margin or edge of the shell, by means of the margin of the mantle, or shell-secreting organ.

Now we shall proceed to show that the schemes of colouration follow out these structure-plans, and thus give additional force to the truth of the classification, as well as showing that, viewed on a broad scale, the present theory is a true one.

We can, in fact, throw the whole scheme into a table, as follows:—

SYSTEMS OF COLOURATION.

	System of Colouring.		Structure.		Sub-kingdoms.
	A.	No Axial Decoration.	A.	No Axial Structure.	A.	Invertebrata.
1.		No definite system.		No definite organs.		Protozoa.
2.		Radiate system.		Radiate structure.		Cœlenterata, Annuloida.
3.		Segmental system.		Segmental structure.		Annulosa.
4.		Marginate system.		Marginate growth.		Mollusca.
5.	B.	Axial Decoration.	B.	Axial Structure.	B.	Vertebrata.
		Axial system.		Axial structure.		Vertebrata.

Protozoa. The protozoa are generally very minute, and always composed of structureless protoplasm. Their peculiarities are rather negative than positive, there being neither body segments, muscular, circulatory, nor nervous systems. Even the denser exterior portion (ectosarc) possessed by some of them seems to be rather a temporary coagulation of the protoplasm than a real differentiation of that material.

Here, then, we have to deal with the simplest forms of life, and if colouration depends upon structure, these structureless transparent creatures should lack all colour-pattern, and such is really the case. Possessing no organs, they have no colouration, and are generally either colourless or a faint uniform brown colour, and through their colourless bodies the food particles show, often giving a fictitious appearance of colouring.