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Note on Merlia normani and the " Monticuliporas." 

 By B. Kiekpateick. 



(Communicated by Prof. Arthur Dendy, F.R.S. Eeceived August 15, 1912.) 



As a result of my recent investigation — carried on with the aid of a grant 

 from the Eoyal Society — of Merlia normani, Kirkp., a siliceous sponge with 

 a supplementary calcareous skeleton, I find that the sponge owes its 

 exceptional character to the fact of its being infested with a Zooxanthella 

 which passes a resting phase in certain cells of the sponge and a motile phase 

 outside those cells. 



All degrees of infection can be seen, from those of sponge cells with only a 

 few monads to stages in which the greatly hypertrophied sponge cells are 

 packed with countless numbers of these organisms. 



The monads in the resting condition have a cellulose-like coat, and in both 

 phases a nucleus and an orange-coloured chromatophor. In the resting phase 

 many undergo division into 2, 4, 8 and probably more cells. 



When masses of sponge cells loaded with monads are examined alive in sea- 

 water in a moist chamber, the monads can be seen escaping from their tests 

 and from the sponge cells and swimming about in the water. 



In this stage, in which they possess two flagella, conjugation can sometimes 

 be observed between cells of different sizes. 



After a period of activity varying from a few minutes to half an hour the 

 motile cells die ; but in place of disintegrating, they become calcified. 



Well prepared decalcified sections of Merlia show that the calcareous 

 skeleton is made up of bricks, each consisting of a calcified corpse of one of 

 these monads. Possibly under normal conditions many of the monads on 

 their escape from the sponge cells become calcified, and added on to the 

 skeleton without passing through the flagellate stage. Merlia is a lineal 

 descendant of the Palaeozoic Monticuliporas, all of which are siliceous sponges 

 with supplementary skeletons formed of the calcified bodies of monads which 

 had lived commensally in the cells of those sponges. The Monticuliporas 

 proper, also species of Chaetetes and Ehaphidopora, all contain siliceous 

 spicules of a kind related to those of Merlia, and, further, the calcareous 

 skeleton is formed on the same plan. 



The monticules of Monticulipora are the expression of sporadic outbursts 

 of activity on the part of • the monads, whereby an extra supply of bricks is 

 formed. Very frequently, Merlia normani is found growing over a 

 Melobesia-like crust, which latter directly encrusts the shell or rock. Even 



