Growth, and Hahits of Coral Zoophytes, Do 



phyllia, Astroides,* Oculina, and Cyathina, some species of 

 which exist in the Norwegian seas. The Gorgonidse, Alcyonidae, 

 Hydroidea, and Actinidse, extend from the equator nearly to 

 the frigid zone. The Bryozoa have an equally wide range-t 



The liability of the lagoons, when contracted in size, to 

 become highly heated by the sun, is probably one cause lead- 

 ing to the depopulation of these internal waters. The tem- 

 perature becomes raised, as in a puddle of standing water 

 elsewhere, and is quite unfitted, therefore, for species accus- 

 tomed only to the ordinary tropical temperature of the ocean. 



Light and pressure, and probably the amount of air in sea- 

 water, influence the growth of corals so far as to fix limits to 

 their distribution in depth. It is a little remarkable that 

 those families which have a wide geographical range have 

 also a great range in depth ; for Carophylliae, Dendrophylliae, 

 Oculinae, Gorgonidse, and Hydroidea, are found even at depths 

 of one or two hundred fathoms ; while Madrepores and As- 

 trseas, and all the ordinary reef-forming species scarcely 

 exceed a depth of twenty fathoms. 



Temperature has little or no influence in determining this 

 range, although it has been so asserted ; QQ° is not met with 

 under the equator short of 75 or 100 fathoms. The follow- 

 ing table gives approximate results for the winter months 

 from observations on this point by diff'erent navigators in the 

 Pacific. It is well known that these averages are varied 

 much in particular regions by currents. 



* The corals of the Astroides closely resemble those of the Astraea, and have 

 been referred to the latter group by many authors. A related species is found 

 on the coast of this country as high up as latitude 42°. An Astraea has been 

 reported from Sydney, New South Wales, which, if a true Astraea (it has not 

 been described or figured), gives this genus a wider limit than the coral-reef 

 seas. 



t See farther, Report on Zoophytes, p. 102. 



