Corals. 



Corals. 



Proceeding from the Actinise we can now more easily under- 

 stand the structure of the Corals. If the Anemones had the power 

 to deposit a calcareous covering on the outside of their body, 

 or a similar skeleton within their body-wall, these hard parts 

 would, after the death of the animal, be termed corals. The fine 

 orange-coloured Coral, Astroides (fig. 52), which lives on the rocks 

 of tank No. 9, may be considered as an Anemone provided with 

 such a calcareous framework. Spreading out their rings of ten- 

 tacles the numerous animals side by side present the appearance 

 of an orange-coloured carpet, but then their framework is not 

 visible. Only after the orange-coloured animal has died and de- 

 cayed away, the remaining grey calcareous skeleton or frame- 

 work becomes visible: this can be seen in several parts of the 

 tank, looking not unlike honeycombs, each comb being the skeleton 

 of a single animal. The coast of Italy is in many places covered 

 with this coral and those who have made by boat the beautiful 

 trip from Amalfi to Scaricatoio will have had ample opportunity 

 of seeing the orange belt it forms on the rocks immediately below 

 the water-line. Similar corals form the large reefs which are 

 met with in the southern seas (even as far north as the Red Sea) 

 stretching often for miles, and several fathoms deep. Their colour- 

 ing is often exquisite. 



Closely allied to Astroides is Dendrophyllia (Fig. 107), the 

 skeleton of which consists of pure white carbonate of lime and 

 forms large branches. The polypes are of the colour of sulphur 

 and comparatively large. In the Aquarium the yellow polyps 

 tend to disappear after a few months and there remains then 

 only the white skeleton, resembling a dead tree, which becomes 

 overgrown by algae and small organisms. One would hardly 

 doubt but that the coral was dead and yet after some months 

 or even after a year the slumbering life revives again, the branches 

 become covered with yellow tissues and at the ends polyps expand. 



The branching of the corals takes place by means of the two 

 methods of reproduction termed "fission" and "budding" respec- 

 tively. In the case of fission one organism splits into two or more 

 parts, each of which will develop into a new complete individual. 

 This process has often been observed to take place ; it has also been 

 successfully brought about by dividing a living animal into suitable 

 pieces, which have then been allowed to grow on and form com- 

 plete polypes. A similar fission takes place in the case of the 

 Coral-polypes, but with this important difference, that the division 

 does not extend down to the base of the animal but that both 

 pieces remain attached to one another ; both give rise to calcareous 

 skeletal substance which naturally remains connected. In this 

 manner arises gradually a coral colony and in the course of cen- 



5 



