IX THE MARKINGS OF ORGANISMS 197 



One region of the corolla, and are associated with 

 irregularity of parts. This is well seen in the mark- 

 ings of orchids, of the foxglove, of pentstemon, and 

 many others, in which cases the parts of the corolla 

 are irregular, and the markings are confined to certain 

 of them. In general, in flowers the markings tend 

 to be similar in homologous parts, but variations in 

 the structure of homologous parts tend to be accom- 

 panied by variation in the colour-patterns. 



Ccelentera. — The colours of Protozoa and sponges 

 are too simple to show any arrangement into patterns, 

 or perhaps it would be more accurate to say that the 

 structure is too simple. In any case, we do not find 

 the phenomenon markedly displayed before we reach 

 the Ccelentera. In them it exhibits itself with the 

 same simplicity seen in plants. The organisms have 

 the radial symmetry so characteristic of flowers, and 

 again we find that homologous parts show similar 

 colouring. One tentacle is in structure and develop- 

 ment like another, and the colours, whether uniform 

 or arranged in simple banded patterns, tend to be 

 identical throughout. As we have already seen, 

 structural differentiation and the development of new 

 colours tend to be associated ; thus knobbed or 

 capitate tentacles usually have the terminal knob of 

 a different colour from the rest of the tentacle — a 

 fact which may be susceptible of a simple physical 

 explanation. Again, when the tentacles are greatly 

 reduced in size, they may cease to behave as in- 

 dividuals in the general colour-scheme, which has 

 then as its unit groups of tentacles. This occurs in 

 the giant anemones (Discosomd), and is of interest 

 because the subordination of the individual coloured 



