Murphology of the Madreporaria. 105 



For the disposition of the musculature and the relation of the 

 complete and incomplete members leave no doubt that the 

 mesenteries numbered / to VI on eacli side are really the 

 protocnemes of the original polyp, and therefore the four 

 JDilateral pairs {A-D) — two complete and two incomplete — 

 on the ventral aspect are new pairs which have been added 

 within the eiitocoele of the primary ventral directives, now 

 pushed widely apart ; and similarly with the two bilateral 

 pairs (/7, F) on the dorsal aspect within the primary entocoele 

 of tlie dorsal directives. 



The accompaniment of fission of the stomodfeal tube, in- 

 volving a separation of the mesenteries attached to it into 

 two series, has really no bearing upon the manner of mesen- 

 terial succession, which alone is sought to be established. I 

 have already carried out investigations on mesenterial deve- 

 lnpn:!ent and stomodfeal fission in the West-Indian corals, 

 Manicina areolata (Linn.), Favia fragum (Esper), and 

 Mceandrina lahyrinthica (Ell, & Sol.), &c. ; but from the 

 beginning the metacnemes in these are added in unilateral 

 exocoelic pairs, as already desciibed for the majority of 

 actinians and corals (fig. 8), and the introduction of fission in 

 no way modifies this method. Fission commences in young 

 ])olyps of M. areoJnta and F. fragum after the third or fourth 

 mesenterial cycle has become established. No new pairs of 

 directives arise in the fission polyps, and the plane of division 

 is not through the directive entocoeles as in Madrepora^ but 

 is usually at right angles to the directive plane. 



During the growth of the second cycle of mesenteries in 

 most corals and actinians the fifth and sixth developmental 

 pairs of protocnemes become complete, but t!iis never happens 

 in the enlarged polyps of Madrepora nor of L'orites', the new 

 pairs are also anisocnemic with the exception of those consti- 

 tuting directives. 



Tlie sequence represented in the three figures is that charac- 

 teristic ot all the polyps examined, but variations in the 

 number of the mesenteries whieh may be relegated to either 

 the dorsal or ventral extremity have been met with. Fig. 7 

 represents a section through a polyp in which three additional 

 pairs (C— £") — two complete and one incomplete — are already 

 added dorsally, and only two pairs (.4, B) — one complete 

 and one incomplete — ventrally. In all the examples pre- 

 viously considered no more than two new pairs are placed 

 dorsally, the remaining four being ventral. The connecting- 

 pair in fig. 1 , whether in the end attached dorsally or ventrally, 

 will separate the two members of a bilateral pair of incomplete 

 mesenteries. From the arrangement of the musculature, and 



