206 MARIA M. OGILVIE GORDON. 
(b) The layer of “ fibre-containing calicoblasts next 
the skeleton.” 
(c) Older layers of similar fibre-containing calicoblasts 
in more and more advanced stages of calcification. 
At the same time, in my work, I took the broad position 
that the ectoderm might be regarded as a many-layered 
structure, the innermost layer being the persistently organic, 
cellular layer of the body-wall, the next Jayers being 
“ calicoblastic,” 1. e. undergoing transformation from organic 
to inorganic condition, each farther layer being more and 
more crystalline. ‘‘ We may look upon the superficial layers 
of the skeletal elements and of incompletely calcified calico- 
blasts as the outer layers of a many-layered ectoderm ” 
(aut., 1. c., p.. 116). 
Mr. Duerden’s description of the relationship of the skele- 
tal laminee to the ectoderm is the same as mine, but he uses 
a different terminology. He follows the precedent of Dr. 
Bourne and others in using the term “ calicoblast” for the 
part of the polypal ectoderm adjacent to the skeletal tissues, 
constantly using the term ‘“ calicoblast ectoderm.” He then 
applies a new term to the next layer of organic tissue in 
which the calcareous crystals are deposited (i.e. the outer 
layer which I called ‘ calicoblastic ”),—describing it as a 
“ homogeneous, mesogloea-like matrix in which the minute 
calcareous crystals forming the skeleton are laid down” 
(Duerden, l. c., p. 84). Then he states that the “ calicoblast 
ectoderm”? does not lay down the skeleton, but that it 
probably secretes this matrix or membrane in which the 
skeleton is laid down. 
Thus Mr. Duerden applies the term “ calicoblast ectoderm ” 
to that which I called simply “‘ ectoderm,” and describes as a 
homogeneous “ matrix,” ‘‘ membrane,” or “‘ sheath” the next 
layer described by me as a layer composed of individual 
calicoblasts in which the crystalline groups made their ap- 
pearance. ‘lhe difference in the use of terms will be evident 
trom the following quotation, where Mr. Duerden describes 
the appearance of the lime-forming layer after decalcification, 
