CORAL ALGAE 211 



cups perforated at the base by a minute aperture 

 which brings them into communication with the labyrinth 

 of spaces in the calcareous matrix of the internodes. The 

 surface pores are therefore continuous with tubes of a lesser 

 diameter which penetrate to the middle of the internodes. 

 This is a feature of some importance, as it is unlike anything 

 that is found in the calcareous structures of animal corals. 



When a piece of fresh or preserved Halimeda is placed 

 in a weak acid and the calcareous matter dissolved, the 

 substance of the plant that remains is found to consist of 

 a bundle of long tubes, sending off a number of branches to 

 the periphery of the internodes and continued into suc- 

 cessive joints through the soft uncalcified nodes. The fine 

 branches of these tubes terminate in swollen cylindrical 

 extremities which are arranged parallel with one another, 

 vertical to the surface, and fit into cups of the calcareous 

 skeleton previously described. 



These terminal swellings of the branches are usually 

 called the " peripheral cells " although the term " cells " 

 is technically inaccurate, for Halimeda and its allies are not 

 strictly cellular Algae, the filaments or tubes of which they 

 are composed being continuous and not broken up by 

 numerous cell walls into cell units. Whether we should 

 call these Algae " non-cellular " or " unicellular," or adopt 

 an altogether distinctive term, is a matter of controversy 

 that can be safely left in the hands of the botanists. 



The characters of Halimeda that have been described 

 are sufficient to justify the separation of the genus from 

 the Lithothamnion group. 



It belongs to the group of the Chlorophyceae or Green 

 Seaweeds and to the family Codiaceae. 



The genus Halimeda is widely distributed in the tropical 

 seas of the West Indies, Indian Ocean, and Pacific Ocean, 

 but also occurs in the Mediterranean Sea and south of the 

 Tropics, on the west coast of Australia, and the east coast 

 of Africa. 



The most widely distributed species is the Halimeda 

 tuna, the original Opuntia marina or Corallina opuntia of 

 the earlier writers. It is the common species of the 



