FORMATION OF THE SKELETON IN THE MADEEPORARIA. 481 



there is a definite aggregation of protoplasmic material Avith 

 reference to the nucleus, a living cell takes form, and each 

 time that, by an act of fi.ssion, an organic, fibre-containing 

 unit is added to the skeletal layer, that unit may be termed 

 the structural equivalent of a cell, although it is not itself 

 living. Some proportion of the nuclear vitality has been 

 employed in the making of each fibre-containing unit. In a 

 word, each calcareous scale represents the product of a 

 nucleated body. 



The most important morphological point in M. Krempf's 

 description is his statement that the nucleated cell is finally 

 transferred ''from the living layer to the skeleton.'^ 

 This has been the real point of controversy. To quote from 

 my work in 1896 : — " Fowler and Bourne have observed the 

 specialised character and large size of the calicoblastic cells 

 at the growing points of the skeleton in several corals, 

 among others Galaxea. Both these authors regard the calico- 

 blasts as ectodermal cells, which merely secrete calcareous 

 substance without being themselves calcified." ..." I find 

 that the cells themselves become incorporated in the 

 skeleton.^' . . . 



On M. Krempf^s own showing, this transferred nucleated 

 cell becomes a calcareous scale, undistinguishable from its 

 neighbours ; in the farther processes of calcification there is 

 no difference between nucleated and non-nucleated skeletal 

 elements.^ 



M. Krempf has given his attention especially to the histo- 

 logical processes, and we may expect a valuable addition to 

 our knowledge of these. The outstanding features in his 



1 It may be of interest to add that in my preparations I sometimes observed 

 traces of nuclei with the organic remnants in calcareous scales ; in some, the 

 reaction to stains was quite marked ; in others, very faint ; and in still 

 others, no nucleus could be discerned by means of stains. I felt I could not 

 draw any secure conclusion as to the absence or presence of the nuclei, 

 and knowing how irregularly they were distributed in the ectodermal tissue, 

 I did not follow this line of observation, but in my published work limited 

 myself to the statement that each "scale " contained organic remnants. 



