CEETATN STICHODACTTlTNiE TO THE MADKEPOEAEIA. 639' 



covered by them on the sea-floor and amongst the coral -rock, 

 and every stage from the single to the many-mouthed condition 

 may be observed. Sometimes one of these latter may be pro- 

 cured in process of complete longitudinal fission, the two parts 

 ultimately separating, each with its own system of tentacles. 



In colonial corals such as Madrepora, Oculina, and Cladocora^ 

 the individual discs are distinct from one another, but the polyps 

 are connected by a thin coenosarc formed, at any rate in the two 

 last, of the united edge-zones or Eandplatten. The disc in each 

 is practically circular, and a system o£ tentacles surrounds but 

 one mouth. 



Amongst the anemones the colonial condition is practically 

 limited to the Zoan these, and all degrees of union are there met 

 with, from the usually isolated polyps of Isaurus to their fusion, 

 with coenenchyme for nearly the whole length of the column 

 as in Palythoa. Species such as Metridium marginatum, which 

 reproduce asexually by longitudinal division, occasionally exhibit 

 two oral apertures at one time, but the condition is never retained 

 for long. Dr. Gr. H.Parker ('Science,' Feb. 1898) estimated 

 the two-mouthed polyps in this species to be in the proportion 

 of about 1 in 700, while Mr. Yau Yleck stated that his experience 

 gave it as 1 in 200 or 300. I have also found the phase to be 

 not uncommon in groups of M. dianthus on the west coast of 

 Ireland. 



In other examples of Actiniaria where asexual reproduction 

 by whatever means occurs, the polyps become separated entirely 

 one from the other. Although the process has been studied in 

 Metridium and other forms, no mention is made of individual 

 polyps remaining connected by a basal coenosarc. Corynactis, 

 however, presents an interesting condition. With regard to the 

 British O. viridis, Gosse states that he has " seen some which 

 were evidently connected together b}^ the base, the process of 

 separation being incomplete "; while in the West-Indian C 

 myrcia I have come upon small groups in which tw^o polyps, even 

 at a little distance apart, were still united by a narrow coenosarc. 

 Taking this in conjunction with other characters yet to be noted 

 in the genus, I regard the phase presented by Corynactis as 

 indicative of a colonial condition in which all the polyps produced 

 asexually remain united by a basal coenosarc, just as in corals 

 like Madrepora and Cladocora. It is apparently an advantage 

 for skeletonless polyps multiplying thus to separate completely. 



