MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 517 



stomodseal tubes, for a time retain this connection throughout the length of each stomodseum. 

 Serial transverse sections indicate that later the middle portion of each connecting mesentery 

 begins to grow radially across the disk, and that when it reaches the vertical column wall it 

 divides into two distinct mesenteries, which constitute a bilateral pair. The division extends 

 all tin 1 way from the upper to the lower termination of the stomodseal tubes, the successive stages 

 in the process being easily followed. As shown by fig. L85, the dorsal connecting mesentery 

 becomes divided and stretches to the column wall in advance of the ventral member. 



That no earlier stages, exhibiting a sequence in the appearance of the six pairs of new 

 mesenteries, have been met with, such as are described for Porites, seems strongly to suggest that 

 the additional six pairs arise practically simultaneously, in all probability pari passu with the 

 division of the primary stomodseum. In the earliest bud polyp of Madrepora which has been 

 obtained, representing a stage before any tentacles appear, all the twelve mesenteries are already 

 present, and the oral perforation appears to have been just established (p. 497). It would also 

 seem that in the formation of new polyps by fission a like simultaneous development takes place, 

 and thus no intermediate' stages between the twelve and twenty-four mesenteries are to be 



expected. 



The results from the two methods of asexual reproduction in coral polyps — budding and 

 fission — may be thus contrasted: 



(1) Polyps arising as buds pass through the same stages as regards the order of appearance 

 of the tentacles, mesenteries, and mesenterial filaments as the larval polyps of the same, species, 

 and the adults of both are alike. 



(■J) Excepting Pontes and Madrepora, polyps originating by discal fission, whether completely 

 or but partly separated, never wholly resemble the sexually-produced polyp. No new pairs of 

 directives are formed, and the mesenteries do not assume a hexamerous or other regular cyclical 

 arrangement. 



(3) Polyps of Porites and Madrepora arising by fission resemble larval polyps in having two 

 pairs of directives and four anisocnemic pairs of mesenteries. (See foot-note, p. 496.) 



SEXUAL REPRODUCTION. 



DISTRIBUTION OF GONADS. 



Although the asexual method plays such a prominent part in coral growth, yet the pro- 

 duction of sexual elements, for the formation of entirely new individuals, appears to be quite as 

 important as in other groups of animals where sexual reproduction alone prevails. In West 

 Indian waters, colonies of Favia fragvm, Manicma areolata, Siderastrsea radians, and Porites 

 clavaria seem to be nearly always fertile, while species of Madrepora, Orbicella, and C'ladocora 

 are, as a rule, found without sexual cells. 



Several observations upon the distribution of the gonads in the Madreporaria have been 

 recorded by other writers, but, as in the Actiniaria, no general rule is apparent with regard to the 

 moncecious or dioecious character of the polyps. Thus Moseley (1N82) found Seriatuporo to be 

 unisexual; Fowler mentions the occurrence of ova only in Madrepora durvillt /\ Turbinaria, sp., 

 and in Sphenotrochusrvbescens, while PocUloporahrevicornis is monoecious. H. V. Wilson merely 

 states that Mdnicina <ir,<,l<it<t is hermaphrodite. Gardiner (1900, p. 367) found all the polyps of 

 < imopsammia which he examined to be female, without any trace of male generative cells. 



In the course of the present studies many instances of fertile polyps have occurred. A 

 portion of a colony of Mseandrina labyrmthica sectionized bore gonads on almost every 

 mesentery, and in this case ova and spermaria were closely associated. In a few instances both 

 kinds of sexual cells are found on the same mesentery (PI. XX, fig. 140), but usually they are 

 developed on separate mesenteries, the number of male mesenteries being greatly in excess of 

 the female. The merest suggestion of an alternation of male and female mesenteries is 

 manifest: thus, one member of a pair may bear spermaria and the other ova. but at other 

 times tw r o or three ova-bearing mesenteries are intercalated between a number of sperm-bearing 



