64 Colouration in Animals and Plants. 



transparent as to be almost imperceptible in water, coenosarc 

 whitish, enlarged portions of polypites, pink or scarlet, sacs of 

 tentacles scarlet. 



The enlarged portion of the polypites is marked with red striae, 

 " which are simply elevations of the endoderm, containing thread- 

 cells and coloured granules." The small polypites do not possess 

 these elevations, and are colourless. 



Agalma breve, like a prismatic mass of crystal, with pink float and 

 polypites. 



Athorybia rosacea, float pink, with radiating dark-brown striae, 

 made up of dots ; polypites lightish red, shading to pink at their 

 apices ; tentacles yellowish or colourless, with dark-brown sacculi ; 

 thread-cells dark brown. 



Rhizophysa filiformis, pink, with deep red patch surrounding the 

 aperture of the pneumatocyst. 



Physalia caravilla, bright purplish-red, with dark extremities, and 

 blue lines in the folds of the crest ; polypites violet, with whitish 

 points, larger tentacles red, with dark purple acetabula, smaller 

 tentacles blue, bundles of buds reddish. 



P. pelagica, in young individuals pale blue, in adult both ends 

 green, with highest part of crest purple, tentacles blue, with dark 

 acetabula ; polypites dark blue, with yellow points. 



P. utriculus. Prof. Huxley describes a specimen doubtfully 

 referred to this species very fully, as follows : — 



" The general colour of the hydrosoma is a pale, delicate green, 

 passing gradually into a dark, indigo blue, on the under surface. 



" The ridge of the crest is tipped with lake, and the pointed end 

 is stained deep bluish-green about the aperture of the pneumato- 

 cyst. 



" The bases of the tentacles are deep blue ; the polypites deep 

 blue at their bases, and frequently bright yellow at their apices ; the 

 velvetty masses of reproductive organs and buds on the under 

 surface are light green." 



He further remarks that the tentacles have reniform thickenings 

 at regular intervals, and " the substance of each thickening has a 

 dark blue colour, and imbedded within it are myriads of close-set, 

 colourless, spherical thread-cells." 



It would not be possible to find a more perfect example of 

 regional colouration. Not only is each organ differently coloured, 



