388 



COELENTERATA ANTHOZOA 



growth of the coral. In other cases, however, further divisions 

 of the stomodaeum occur before the separation of the zooids, and 

 then elongated, serpentine polyps are produced (as in Meandrina, 

 etc.), which consist of a number of imperfectly separated zooids, 

 each with a distinct mouth and stomodaeum but with continuous 

 coelenteric cavities. Two kinds of fission must be distinguished 

 from each other. In Madrepora and Poriies the plane of fission 

 passes dorso-ventrally through the zooids, that is, between the 

 dorsal and ventral pairs of directive mesenteries. In these cases 

 the zooids produced by fission are similar to the parent form. 



Fig. 170. — Diagrammatic transverse sections oi Porites to illustrate the process of fission. 

 A, before division ; B, fission nearly completed. In A four bilateral pairs [a, b, c, d) 

 of mesenteries have appeared in the entocoele of the ventral directives ( VD). These 

 are increased to six pairs and then fission commences as seen in B, the plane of 

 fission passing through the entocoeles of the last pair of secondary mesenteries (/) 

 and of the dorsal directives (DD). I, II, V, VI, the protocnemes in the order of 

 their development. (After Duerden. ) 



In most Madreporaria, however, the plane of fission appears to 

 be more or less at right angles to this, and the resulting zooids 

 are unlike the original parent form in having either no directive 

 mesenteries at all or only one pair of them. 



The section Fungacea presents us with some exceptional and 

 remarkable forms of asexual reproduction. The embryo Fungia 

 gives rise to a conical fixed coral called a " trophozooid." The 

 upper part of the calyx of this trophozooid expands and becomes 

 disc-shaped. This is called the " anthocyathus," and after it has 

 reached a certain size it breaks away from the rest of the tropho- 

 zooid as an adult Fungia. Several anthocyathi may be formed 

 in succession from one trophozooid. This may be described as 

 a process of successive transverse fission. In Diaseris the disc 

 divides into four quadrants, and each quadrant appears to be 

 capable of acquiring the shape and size of the undivided parent. 



