POLYZOAN CORALS 173 



to assist the collector to distinguish the Polyzoa from other 

 corals. But the scope of the present work does not permit 

 any attempt to be made to give such a detailed account of 

 the very large number of genera which are included in the 

 group as will enable him to identify his specimens and give 

 them the correct names they should bear in his collection. 

 Both the Orders of calcareous Polyzoa, but particularly the 

 Cheilostomata, present many difficulties for the systematist. 

 Like many other animals that lead a sedentary life and form 

 plant-like colonies by the rapid asexual reproduction of the 

 polyps, there is a very wide range of variation in the general 

 form and in some of the details of structure, so that there 

 is some difficulty in drawing the boundary lines between 

 closely related genera and species. It is necessary, there- 

 fore, for the naturalist to consult the special memoirs on the 

 group 1 if he wishes to get the correct names for his specimens. 



From the frequent references that have been made to 

 the occurrence of calcareous Polyzoa off the British coasts it 

 may be inferred that this group of corals is well represented 

 in the waters of the temperate regions of the world. It is 

 not necessary for the naturalist to visit the coral reefs of 

 the Tropics if he wishes to find abundant material for their 

 study. He will be able to discover as rich a fauna of this 

 description in European waters as anywhere else. 



The warmer tropical waters of the world might seem to 

 be less favourable for the growth of Polyzoa, because these 

 relatively small corals are apt to be lost sight of among the 

 bewildering complex of huge and fantastic zoophytes of 

 other Orders that are crowded together in every locality of 

 the sea-bottom that is suitable for the growth of corals. 

 But it has been shown that when the marine fauna of tropical 

 waters is carefully and criticall}' examined a great abundance 

 and a great variety of calcareous Polyzoa can be found. It 

 is probably not a fact that tropical water is unfavourable 



1 T. Hincks, History of the British Marine Polyzoa, 1880 ; G. R. Vine, 

 Report on Recent Marine Polyzoa : Reports of British Association Meeting 

 at Aberdeen, 1885, vol. Iv. References to more recent memoirs and 

 treatises will be found in the works of JuUien and Calvet ; Campagnes 

 scientifiques du Prince de Monaco, fasc. xxiii., 1903, and S. F. Harmer, 

 Reports of Siboga Expedition, livr. Ixxv., 1915. 



