ZOANTHARIA — MADREPORARIA 



389 



Without doubt a process of sexual reproduction occurs in all 

 Madreporaria. In some genera sexual reproduction appears to 

 be almost continuous throughout the year ; in others the sexual 

 organs are formed only at periods separated by considerable 

 intervals of sterility. According to the researches of Duerden 

 the Madreporaria appear to 



be usually -viviparous, the ^,^=::;$S:S^\\\j/i'//r^^ Cy. 



early stages of development ■^^^'>^'^^\< 'W/''^^'^'^^--^^'^:^ -•" ^' 

 are passed through within the 

 body of the parent, and the 

 young coral is discharged 

 into the water as a free- 

 swimming ciliated larva. The 

 larvae are spheroidal, oval, or 

 pear-shaped, but change their 

 shape a good deal, and some- 

 times become elongated, 



straight, or spirally twisted Fio. 171. — a fixed stage in the development 



^„ ■]„ rrii 1 J. £ i. "f Fungia. The trophozooid has become 



rods. Ihe larvae are at first differentiated into a discoid crown, the 



dense and opaque, but Subse- anthocyathus (ay) and a pedicle, the antho- 



,1 , , , , . caulus (Ca). (After G. C. Bourne. ) 



quently they become dis- 

 tended by the absorption of water, and more nearly transparent. 

 They swim about for one or two days, and then settle down by 

 the aboral pole and become fixed. The tentacles are not formed, 

 in any species that has yet been observed, during the free- 

 swimming stage of existence. 



Distribution of Reef Corals. — The principal reef-forming 

 corals reach their greatest size and grow with greatest rapidity 

 in the warm, shallow waters of the world, but they are not 

 confined to this habitat. A species of Madrepora has been 

 found in the very cold waters of Archangel, and Manicina areolata 

 occurs in Simon's Bay, Cape of Good Hope, many degrees south 

 of the region of the East African coral reefs. As regards the 

 distribution of these corals in depth, very little is known at 

 present. The face of the growing coral reef that is turned 

 towards the open sea is so steep that it has been found 

 impossible to determine to what depth the living reef corals 

 actually extend. 



The survey of the Macclesfield bank proved that a consider- 

 able number of reef corals are to be found alive at depths 



