34 PERCY SLADEN TRUST EXPEDITION 



pp. 152 and 153). Later he adds that m fissiparous gemmation "the division of the 

 stomodaeum has not the same significance as in true hssiparity. It is rather a separation 

 of two distinct stomodsea, one belonging to the parent and one to the bud ; whereas, in 

 true fission, it is the division of an enlarged stomodaeum into halves, and neither represents 

 a distinct individual." 



From this it is evident that Duerden's original ideas of fission and budding did not 

 fit in with certain facts that were observed later, and as a consequence he had to modify 

 them to such an extent that the processes came to merge into each other as far as 

 his ultimate results are concerned. Moreover, in some of my species in which extra- 

 calicinal budding is the commoner method of asexual reproduction, e.g. Favia versijwra 

 (Lam.) and Favia ivakayana (Gard.), directive mesenterial couples are absent, and hence 

 it follows that even true gemmation need not always be followed by the presence of 

 directives and the regular cyclical arrangement of the mesenteries. 



Whatever may be the exact morphological changes involved in the two processes, in 

 this paper "gemmation" is used to denote the development of a polyp outside the 

 tentacular ring of its parent, viz. from the edge-zone or coenosarc, the new individual 

 being a new growth and hence termed a "bud." " Fissiparity " signifies the formation of 

 fresh polyps inside the tentacular ring, viz. in the oral-disc area of an older polyp, the 

 former being only parts of the latter separated off. Following this distinction all extra- 

 calicinal buds would be true buds, while the various types of intra-calicinal buds would be 

 regarded as fission-products. 



The presence of two couples of directive mesenteries is invariably associated in my 

 polyps with two types of symmetry, viz. (l) bilateral symmetry, along two vertical planes, 

 indicated by the lateral compression of the stomodaeum, by the presence of a directive groove 

 and by a directive couple of mesenteries at each end of its longer axis ; (2) hexameral 

 symmetry, shown by each of the alternating mesenterial cycles consisting of six couples or 

 of a multiple of six. 



Conversely the absence of the directive couples is marked by the disappearance of 

 the two symmetries, the only distinction in the arrangement of the mesenterial couples 

 being between those which meet the stomodaeum and those that do not reach it. 



In the fission-products of the genera I have studied the stomodaeum appears to arise 

 in two ways : (l) as an invagination of the oral-disc* of another polyp, i.e. as an 

 independent structure secondarily effecting a communication with the gastro-vascular 

 cavity, e.g. in Favia ahdita (Ell. and Sol.); (2) as a diverticulum from a parent stomodaeum 

 which grows towards the oral-disc and opens to the exterior, as is probably the case in 

 Goniastrea pectinata (Ehrb.). 



In the case of either of the two processes I have suggested, some of the mesenterial 

 couples of the old polyp would secondarily become attached to the stomodaeum of the new 

 individual, and to the latter would come to belong also the tentacles which arose from the 

 chambers between such mesenteries. 



Astrseidse with distinct corallites. Duerden bases his classification of the Madrepo- 

 raria upon what he considers to be two distinct types of mesenterial succession (32, 



* This process is somewhat similar to the stomodseal formation in Flabellum as conceived by Gardiner. 



