52 Colouration in Animals and Plants. 



terata are transparent animals, but it is amongst them we first come 

 across opaque colouring. 



Of the lowest forms, the hydras, nothing need be said here, as 

 they are so much like the protozoa in their simplicity of structure. 



The Corynida, familiar to many of our sea-side visitors by their 

 horny brown tubes (Tubularia), attached to shells and stones, are 

 next in point of complexity. Within the tube is found a semi-fluid 

 mass of protoplasm, giving rise at the orifice to the polypite, which 

 possesses a double series of tentacles. These important organs are 

 generally of a vivid red colour, thus emphasizing their importance 

 in the strongest manner. Other members of the order are white, 

 with pink stripes. 



In the larval stage many of the animals belonging to the above 

 and allied orders, are very like the true jelly-fishes. These free 

 swimming larvse, or gonop/iores, possess four radiating canals, passing 

 from the digestive sac to the margins of the bell, and these are often 

 the seat of colour. In these creatures, too, we find the earliest 

 trace of sense organs, and consequently, the first highly differen- 

 tiated organs, and they appear as richly coloured spots on the 

 margins of the bell. The true oceanic Hydrozoa again afford us 

 fine examples of structural colouration. The beautiful translucent 

 blue-purple Velella, which is sometimes driven on to our shores, is a 

 case in point ; and its delicate structure lines are all emphasized in 

 deeper hues. The true jelly-fishes (Medusidce) with their crystal 

 bells and radiating canals, frequently show brilliant colour, and it is 

 applied to the canals, and also to the rudimentary eye-specks, which 

 are frequently richly tinted, and in all cases strongly marked. In 

 the so-called "hidden-eyed" Medusae we find the same arrangement 

 of colour, the same emphasized eye-specks, and the reproductive 

 organs generally appear as a vivid coloured cross, showing through 

 the translucent bell. 



Turning now to the Actinozoa, of which the sea anemonies and 

 corals are types, we are brought first into contact with general 

 decorative, more or less opaque colour, applied to the surface of the 

 animal. In the preceding cases the animals have been almost 

 universally transparent or translucent, and the colouration is often 

 applied to the internal organs, and shows through. In the sea- 

 anemonies we find a nearer approach to opacity, in the dense 

 muscular body, though even this is often translucent, and the 

 tentacles generally so, often looking like clouded chalcedony. The 



