CHAPTER VII. 

 Colouration in the Invertebrata. 



IF the principle of the dependence of colour-pattern upon struc- 

 ture, enunciated in the preceding pages be sound, we ought to 

 find certain great schemes of colouration corresponding to the great 

 structural subdivisions of the animal kingdom. This is just what we 

 do find; and before tracing the details, it will be as well to group 

 the great colour-schemes together, so that a general view of the 

 question can be obtained at a glance. 



The animal kingdom falls naturally into two divisions, but the 

 dividing line can be drawn in two ways. If we take the most 

 simple classification, we have : — 



1. Protozoa, animals with no special organs. 



2. Organozoa, animals possessing organs. 



Practically this classification is not used, but we shall see that 

 from our point of view it is a useful one. In the most general 

 scheme the divisions are : — 



1. Invertebrata, animals without backbones. 



2. Vertebrata, animals with backbones. 



The invertebrata are divided into sub-kingdoms, of which the 

 protozoa form one. These protozoa possess, as it were, only negative 

 properties. In their simplest form they are mere masses of proto- 

 plasm, even lacking an investing membrane or coat, and never, 

 even in the highest forms, possessing distinct organs. It is this 

 simplicity which at once sepai*ates them entirely from all other 

 animals. 



