LIME-FORMING LAYER OF MADREPORARIAN POLYP. 211 
eminence of the growth-lamella assumes a hemispherical, 
conical, or any other form, according to the shape of the 
ectodermal pit... . Im all cases the fibres radiate around 
what was formerly the axis of the pit. By continuous 
deposition of lamelle a fascicle of fibres is determined, 
whose axis coincides with this axis” (aut., ].c., p. 137, cf. 
p. 159, etc.) 
Mr. Duerden writes, ‘I conceive that the so-called centre 
of calcification is really the organic centre or axis around 
which the skeletal matter is deposited in a radiating or 
feather-like manner, and that at an early stage in the living, 
growing skeleton, the centre is occupied by the mesoglcea- 
like matrix, within which it has been shown that the cal- 
careous fibro-crystals are deposited” (Duerden, 1. c., p. 43). 
This interpretation of the “dark points” and “ dark lines” 
does not differ from mine in so far as relating them to organic 
residual fragments of an organic layer undergoing changes of 
calcification. 
Further, my explanation (aut., 1. c., p. 113) of the cause of 
the appearance of dark and light bands in the succession of 
erowth-lamelle, viewed by transmitted light, is the same as 
given by Mr. Duerden on p. 42 of his work; the margins of 
“dark, finely-granular particles, similar to those at the 
centres of calcification,’ having been detected by me and 
their significance interpreted as all-important evidence in my 
demonstration of the separation of successive calicoblast or 
lime-forming layers, and the gradual transformation of each 
to build up askeletal growth-lamella (cf. Duerden, p. 44; 
Ogilvie, pp. 111, 150, fig. 30s.) 
