CALCAREOUS SKELETON OP THE ANTHOZOA. 539 



after holding almost every other conceivable hypothesis on the 

 subject. The corallum of the Madreporaria and of Heliopora, 

 and the spicules of other Alcyonaria, are crystalline growths 

 formed by the deposition of needles of carbonate of lime in a 

 colloid matrix, and obeying the ordinary laws of crystalline 

 growth in detail ; but the general arrangement of the fasciculi 

 of crystals is dominated, in some manner of which we are 

 ignorant, by the living tissues which clothe the corallum. 



We have seen that the characteristic structure of certain 

 Alcyonarian spicules is moulded upon an organic pattern of 

 fibres. I have looked for a similar organic pattern in Madre- 

 poraria, but without success. The corallum of Madrepores is 

 invariably penetrated by the mycelium of the parasitic fungus 

 which I have elsewhere described under the name given to it 

 by W. B. Carpenter, Achyla penetrans. I believe, how- 

 ever, that it does not really belong to the genus Achyla. 

 However, the presence of these fungus filaments have pre- 

 vented my making any trustworthy observations on the organic 

 matrix of the Madreporarian skeleton. I have slowly and 

 carefully decalcified sections of coralla on a slide, and have 

 invariably obtained a plexus of mycelial filaments, among 

 which I could detect fine threads whose arrangement I could 

 not determine owing to the presence of the fungus. I am of 

 the opinion that there is an organic pattern, probably con- 

 sisting of a fine network of threads analogous to those observed 

 in the spicules of Spongodes, but I cannot at present say 

 anything definite on the subject. Further, I STispect that the 

 dark " centres of calcification " will be found to be the ex- 

 pression of a core of organic filaments, just as the central dark 

 line in the Alcyonarian spicule is the expression of the central 

 core of threads. In further support of the conclusions arrived 

 at as to the formation of the Madreporarian skeleton, I must 

 add that the " scales" which are so conspicuous in Galaxea, 

 and in the genus Madrepora, as also in Muss a and some 

 other genera, are by no means a constant feature in Madre- 

 poraria. I have failed to find them in Caryophyllia, 

 Porites, Montipora, Lophohelia, and others. I have 



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