LIME-FORMING LAYER OF MADREPORARIAN POLYP. 205 
any comparative reference to Mr. Duerden’s work and mine 
a difficulty arises from our different use of the term 
* calicoblast.” 
Von Heider, from his observations of the coral polyp, 
advanced the idea that the skeletal matter was laid down 
within certain cells, and he termed these cells “ calico- 
blasts,” or “lime-forming cells.’ Subsequent zoological 
writers insisted that the calcareous matter was secreted by 
the ectoderm, and Jaid down outside it, nevertheless they 
adopted von Heider’s term “ calicoblast,” using it for the 
ectodermal cells in these parts of the polypal body-wall out- 
side which the calcareous skeleton was deposited. This 
adoption of von Heider’s term by zoologists who upheld the 
principal of deposition of the limy skeleton external to all 
organic tissues was, In my opinion, inappropriate, and has 
been very misleading in the literature. 
When I succeeded in separating the skeletal unit with its 
minute group of calcareous crystals and its organic residue, 
and found its size corresponded on the one hand with that of 
an ectodermal cell, on the other with the breadth of a 
skeletal lamella, I considered it to be the true representative 
of von Heider’s “ calicoblast,” and applied the term to it. I 
never applied von Heider’s term to an ectodermal cell in 
the ectoderm, but strictly to the unit-component of the 
skeletal layers, saying that the unit-component was the 
product of an ectodermal cell, was at first entirely organic, 
but that afterwards a group of calcareous crystals developed 
within it, and the “outlines of the individual calicoblasts 
became vaguer as their calcification was more complete.” I 
showed that “each skeletal lamina (average width ‘003 to 
‘005 mm.) was originally a deposit of calicoblasts,” the calico- 
blastic laminze in the septum being an exact replica in form 
of the ectoderm of the polyp (aut., l. c., pp. 115, 117, 124, 
127, 187, etc.). 
Thus I discriminated between :— 
(a) The ectodermal cell-layer from which a series of 
calicoblastic layers takes origin. 
