22 Coelenterata. 



there are also aggregations, a large specimen being surrounded by a number 

 of others all smaller but practically uniform in size. Both anemones extrude 

 larvae very freely and the patches are mainly formed of individuals derived 

 from such larvae as settled near the parent. Similar extensive patches of 

 Stoichactif; helianthus are not infrequent and are probably due to the same 

 cause, as asexual reproduction seems to be very rare in this species. 



Duerden( 5 ) finds, in nearly all fresh and preserved corals, perforating 

 algse in great abundance. The green algse (Gomontia, Ostreobium] are more 

 frequent than the red one. No fungus was found. The nonseptate green alga 

 (Ostreobiwn) bears the closest resemblance to the figures of Achyla penetrans 

 given by Duncan and Bourne and will probably be identical with the latter. 

 Similar algse were found in corals from the Pacific and in a Tubipora. The 

 process of algal corrosion seems to play an important part in the disinte- 

 gration of coral masses. "Rottenness" in corals is largely due to the solvent 

 action of these alga? aided by boring animals. 



Duerden( 6 ) gives an account of the significance of budding and fission in 

 Madreporaria. The following genera of colonial corals all reproduce asexually 

 by budding from one region or another of the polypal wall: Acropora 

 (Madrepora), Porites, Astrangia, Phyllangia, Cladocora, Orbicella, Solenastrcsa^ 

 Stephanocamia, Oculina and SiderastraM. The bud polyps of such gemmiferous 

 corals arise as new individuals. In the course of their development they pass 

 through the same stages as larval polyps and ultimately possess all the distinc- 

 tive characteristics cyclical hexameral plan and directive mesenteries - - of 

 sexually produced polyps. Favia, Dichocosnia, Isophyllia, Manicina, M<zan- 

 drina, Pectinia and Colpophyllia all reproduce asexually by fission, not by 

 gemmation. Larval polyps of fissiparous corals at first present a regular cyclical 

 hexameral arrangement of the mesenteries, tentacles and septa. The first 

 fission partially or wholly divides the polyp into two practically equal parts 

 in an entoccelic plane at right angles to the directive plane, each half having 

 only one pair of directive mesenteries. In the later growth new mesenteries 

 arise in isocnemic pairs more rapidly in some regions than in others and thus 

 destroy the regularity of the cyclical hexameral plan. Additional oral aper- 

 tures and stomodsea, with which a variable number of mesenteries are asso- 

 ciated, arise at somewhat regular intervals. The various stomodseal systems 

 may remain in continuity with the common coelenteron, or partitions may be 

 formed in greater or less number and lead to their partial or complete sepa- 

 ration. No new pairs of directives ever arise, so that however large the 

 polypal system may become, never more than the two primary pairs of 

 directives are present. These are situated at the two morphological extremities 

 of the colony. The entire polypal system of a fissiparous coral, however 

 large, is not made up of individual polyps but is an enlarged complex growth 

 of the primary larval polyp in which new oral apertures have been formed to 

 meet physiological needs ; morphologically it is only a single complex polyp 

 as contrasted with a gemmiferous colony which is made up of numerous polyps. 



Duerden( 9 ) describes the anatomy and histology of West Indian Madre- 

 porarian polyps. The ectoderm of the column rarely if ever contains 

 recognisable muscle and nerve fibres and its nematocysts are never in batteries. 

 The endoderm consists mainly of gland cells, its ciliation is feeble, and in 

 the lower regions of the polyp the endoderm loses its distinctly cellular character 

 appearing finely reticular and so greatly thickened that it often nearly obli- 

 terates the coelenteron. Large oval nematocysts occur in the endoderm of 

 Porites and Madrepora, the numbers and distinctive form of which show that 



