606 APPENDIX 



Into the single body-cavity of each polyp project eight radial partitions, the outer 

 ends of which are united to the body- wall and the inner to the stomodaeum or gullet. This 

 opens to the exterior in the mouth, which is surrounded by eight tentacles. The nourishing 

 of the polyp is performed by the ingestion of food into the body-cavity. The. rapid and 

 continual motion of the tentacles induces currents in the sea-water which sweep small 

 organisms of all kinds into the mouth, down the gullet, and into the body-cavity of the 

 polyp, where they are digested, forming a white milk-like fluid. This circulates in a com- 

 plicated system of tubes throughout the ccenosarc, so that all members of the colony share 

 equally, and none is better nourished than another. The fine grooves so characteristic of the 

 surface of natural coral are due to this tube-system ; they correspond to vessels lying in the 

 innermost part of the ccenosarc, close to the skeleton. 



Reproduction takes place in two ways, by budding and by the development of eggs. 

 Bv budding, new individuals in an already established colony are formed, while from each 

 eu-g arises a perfectly independent daughter-colony. The polyps of a single stock are 

 usually all male or all female, but occasionally polyps of both sexes may be found in the 

 same colony, though, as a rule, on different branches. The fertilising cells of the male are 

 discharged into the water and eventually find their way into the body-cavity of a female. 

 The eggs of the latter after fertilisation develop into small oval larvjE scarcely visible to the 

 naked eye, which escape through the mouth of the parent, and for a time swim about freely 

 in the sea. After a time each larva attaches itself to some suitable object on the sea-bottom 

 and gradually assumes the form of an adult polyp, which by repeated budding forms a 

 colony. 



The first stage in the development of the polyp after the fixation of the larva, is the 

 appearance of a tiny knob or swelling upon the free end. This becomes gradually larger 

 and larger, and, as calcareous spicules appear in its substance, assumes a red colour, finally 

 becoming transformed into a perfect adult polyp. This transformation is accompanied by 

 the deposition of calcium carbonate in a circular area of the surface of attachment of the 

 polyp, and the formation of the foot, the organ of attachment of a coral-colony. During 

 the development of the colony, calcium cai-bonate is continuously separated out from the 

 sea-water and deposited in the living ccenosarc in the form of spicules. These become 

 embedded in a dense calcareous, cement-like substance and thus the hard, axial skeleton of 

 the colony is formed. This continually increases in diameter by the deposition of fresh 

 layers of calcium carbonate, and gives off' new lateral branches with the development of new 

 polyps. The foot also, which is invested by ccenosarc, increases in circumference pro- 

 portionately with the increase in size of the colony. The laminated structure of the coral 

 skeleton points to the fact that the deposition of calcareous matter does not proceed 

 uninterruptedly, but that periods of activity alternate with periods of rest, these periods 

 being possibly seasons of the year. Thus each layer of calcareous material corresponds to 

 a period of activity, and the interruption between successive layers to a period of quiescence. 

 The coral -skeleton grows also in length as well as in diameter, for fresh material is always 

 being deposited at the free ends of the stem and branches. 



At an early stage in its development the coral-colony consists only of one polyp, but, by 

 a process of budding, multiplication of the polyps and the formation of a larger or smaller 

 colony is effected. The new polyps arise at various spots in the ccenosarc as knob-like 

 swellings, which gradually unfold, take on the characters of the adult, and perform their 

 share of the work of nutrition and reproduction. The process suggests the formation 

 and unfolding of a leaf-bud, and for that reason is known to zoologists as budding or 

 gemmation. 



