CORALS. 



5°5 



SIMPLE coral, Thecocyathus 

 (nat. size). 



to consider those corals which do not typically form stocks, but remain at the stage 

 of a simple sea-anemone, only with a rigid, calcareous skeleton supporting, and no 

 doubt protecting, them in different ways. All the corals found in British seas are 

 (with the exception of the so-called tuft-coral) single, and generally very small. As an 

 example of a regular, circular, solitary coral, we may take Thecocyathus cylindraceus, 

 the skeleton of which is shown in the illustration. The 

 animal when expanded fills up the central depression, but 

 when, on expelling the greater part of the watery contents 

 of its cavity, it contracts, the whole body seems to sink 

 into the hollow cup formed by its skeleton. In the 

 illustration we see only the outer wall and the top of the 

 ring of septa, which are solid vertical plates, rising up 

 from the pedestal secreted by the foot and radiating out- 

 wards in all directions. Two other solitary corals are 

 worth describing, as they show certain interesting special- 

 isations. Both of them may increase by budding, that is, 

 by the method which, in colony-forming corals, leads to the 

 formation of stocks, if the buds remain attached to their parents. When, however, 

 solitary corals bud, the buds fall off, and lead solitary lives like their parents. 



Most of the numerous species of the scarlet crisp-corals (Flabellum) are 

 individuals, and are characterised by the slit-like form of the mouth. At a in the 

 illustration the living animal is seen from above, while b shows a side view of the 

 skeleton, which is attached. It resembles a pair of fans fastened along their edges ; 

 and just inside the outer edges of the fans is the row of tentacles. The whole 

 animal is as if the upper end of a circular polyp had been squeezed, so that the 

 mouth-area, instead of being round formed a long oval (a). An interesting case of 



budding occurs in these corals, 

 the buds falling off! In the 

 illustration, c shows the bud 

 growing out at the top of an 

 individual like b. In this 

 budding condition the coral 

 might pass for a different species 

 of Flabellum. The bud, how- 

 ever, ultimately falls off* (d), but 

 instead of becoming attached, 

 is swept by the waves into some 

 rocky fissure, where it spends the 

 rest of its life. Besides the fact 

 that it remains unattached, this bud differs from its attached parent in a far more 

 important respect. It can produce eggs, which the fixed coral can not do, so that 

 we have here another case of alternation of generations. Out of the egg comes 

 an attached form, which buds and produces the free unattached form, which again 

 produces eggs, and so on. The predominating colour of this species is a beautifully 

 intense and yet transparent red, the mouth-disc having almost always broad bands 

 of darker red, most marked in the paler specimens. 



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scarlet crisp-coral, Flabellum (nat. size. 



