Colouration in the Invertebrate. 55 



It must be remembered that in these cases the colour seems 

 actually to be intentional, so as to form a real and not merely an 

 accidental contrast between the stony polypidom and the polyp, for 

 the connecting tissue (ccenosarc) is itself as colourless as it is 

 structureless. 



Gathering together the facts detailed in this chapter we find : — 



1. That the Protozoa are practically colourless and structureless. 



2. That in those species which possess a rudimentary organ 

 (contractile vescicle) a slight decoration is applied to that 

 organ. 



3. That in the Coelenterata the colouration is directly dependent 



upon the structure. 



4. That in transparent animals the colouration is applied directly 



to the organ whether it be internal as in the canals or 

 ovaries, or external, as in the eye-specks. 



5. That in opaque animals, as in the sea-anemonies, the colouring 



is entirely external. 



6. That it is very variable in hue, but not in pattern. 



7. That the most highly differentiated parts (tentacles, eye- 



specks), are the most strongly coloured. 



8. That in the corals an emphatic difference occurs between the 



colour of the polypidom (or " coral ") and the polyp. 



