506 



COELENTERA TES. 



The mushroom-corals (Fungiidce) are another remarkable group of solitary 

 forms, taking their name from their resemblance to the head of an expanded mush- 

 room turned upside down. Turning to the figure of Thecocyathus (on p. 505), and 

 imagining the circular wall pulled down all round, and drawing down the septa so 



that they radiate outwards, some idea of a Fungia may 

 be obtained. Their skeletons are remarkable objects, which 

 no one, at first sight, would in any way connect with a sea- 

 anemone. Although the mushroom-corals are considered 

 to be individuals, reproducing themselves by means of 

 eggs, both budding and division into halves occur excep- 

 tionally ; in the former case the buds sooner or later 

 becoming detached. In some there is an alternation of 

 generations, leading to the formation of compound stocks. 

 In the illustrated form true mushroom-corals are produced 

 at the ends of the branches; at a one has become detached, 

 mushboom- coral budding and an( j the others are in different stages, the youngest being 



FOBMING A SMALL STOCK , ,. , . , ,.', , . , , , ,. , , 



(nat size) nearly cylindrical, like a typical polyp, whereas the older 



ones spread out like a typical Fungia. When a bud has 

 fallen off, the stem seems capable of developing another. This is the asexual genera- 

 tion, reproduction by eggs being the sexual generation. Lastly, certain solitary corals 

 have recently been discovered in the deep sea, where, on account of the presence of 

 carbonic acid in suffi- 

 cient quantities to 

 make itself felt, there 

 is little lime. On this 

 account the calcareous 

 skeleton is generally 

 distinguished by great 

 delicacy. A deep-sea 

 coral with such a deli- 

 cate skeleton (Lepto- 

 penus), found off the 

 east coast of South 

 America at a depth of 

 over a mile, is shown 

 in the illustration. Its 

 pedestal is formed of a 

 delicate network with 

 fine rays or spokes, 

 connected together in a 

 regular manner by 

 transverse supports. 



Plentiful as are the solitary corals, they are surpassed in number by those 

 which form compound stocks ; that is to say, in which the buds do not fall off but 

 go on budding till coral-islands and barrier - reefs are built up. As it is im- 

 possible to give here more than a very few illustrations of the many different ways 



A deep-sea coral, Leptopenus discus (nat. size). 



