PROTOZOA, CCELENTERA, AND ECHINODERMA 95 



growing coral at a depth of forty- four fathoms in the 

 China seas ; but, nevertheless, it is perfectly true that 

 the corals do not grow in such profusion in very deep 

 water as to form anything that can be compared with 

 the reefs of the shores. It is quite possible that the 

 advantages afforded by the light, warmth, and abun- 

 dance of food of the shallow water may account for 

 the luxuriance and vigour of the reef corals, and that 

 where the food is scarce, and the water cold and dark 

 as it is below fifty fathoms, the power of continuous 

 gemmation is lost, and the rapidity of the growth and 

 reproduction of the individual polyps is considerably 

 diminished. 



The fact remains, however, that, as with the sea 

 anemones, so with the madrepores, nearly all the 

 great divisions have a few isolated representatives in 

 the abyss, and that no great family occurring in large 

 numbers has yet been discovered peculiar to this zone. 



The Alcyonaria, on the other hand, do present us 

 with at least one example of a true deep-sea family. 

 This great class of Anthozoa, distinguished from the 

 Zoantharia by the presence of not more than eight 

 tentacles and mesenteries and by the pinnate character 

 of the former, falls into four principal divisions. The 

 Stolonifera, the Alcyonidse, the Gorgonidse, and the 



