SEA-ANEMONES AND THEIR ALLIES. 75 



Though perhaps not a strictly littoral form, in sheltered 

 situations large colonies may often be found between tide- 

 marks, usually in company with Actinoloba diantlms. 

 Probably in both cases shelter from violent wave-action is 

 indispensable, and it is only where this is attainable that 

 life in the littoral zone becomes possible for either. Small 

 colonies with a diameter of perhaps J inch to J inch are 

 often common in rock pools, but the full-grown colonies form 

 bulky lobed masses, several inches in height and diameter. 

 The fleshy substance (ccenosarc) is yellow or pinkish, but 

 the polypes themselves are clear and colourless. They each 

 bear eight tentacles, while sea-anemones have their tentacles 

 in multiples of six. Further, each tentacle is pinnate, or 

 fringed with small processes arranged like the barbs of a 

 feather, the result being to produce a beautiful star-like 

 crown when the tentacles are spread out in the water. The 

 internal anatomy generally resembles that of sea-anemones, 

 and some of its details may be made out through the 

 transparent body-wall. Each polype is placed in a small 

 cavity of the pulp or ccenosarc, into which it may be 

 retracted. The coenosarc contains a series of canals, which 

 place the polypes in communication with one another, and 

 is strengthened by limy spicules scattered through its 

 substance. 



Eelated to Alcyonium is the very beautiful sea-pen (Pen- 

 natula phospJiorea), which occurs freely in deep water, and 

 may sometimes be obtained from the fishing-boats. It is in 

 the form of a fleshy plume of red colour, the upper region 

 bearing numerous polypes like those of Alcyonium. It has 

 a central rod of lime in its lower region, and so leads up to 

 the red coral of commerce, which is in reality the supporting 

 axis of a fleshy coenosarc bearing numerous polypes like 

 those of Alcyonium. It thus differs markedly from the 

 majority of the " corals " which are made by the aggregation 

 of many limy cups containing polypes ; that is, are built on 

 the same plan as the horny skeleton of a Campanularian. 

 In the red coral there are no cups, for the polypes are placed 

 in a fleshy ccenosarc, as in Alcyonium^ this being removed 

 during the process of preparation of the coral. It may 

 perhaps be well at this point to spare a few words to repeat 

 that "corals" are the hard parts of Ccelentera, and there- 



