204 MARIA M. OGILVIE GORDON. 
poraria know that, previous to my work, the ectoderm was 
said to consist of a single layer, and the calcareous skeleton 
to derive origin from this ectoderm by secretion. As Koch 
wrote, “ The ectodermal cells actively separate out calcareous 
matter, and at the same time continue their own existence.” 
I found that in all variations of form, from the simple dis- 
sepiment to the highly decorative row of granulations on many 
septa, the calcareous skeleton had a quite particular relation- 
ship to the polypal wall, and that the skeletal lamelle were 
composed primarily of a number of minute, crystalline, cal- 
careous groups, in size closely corresponding to that of the 
ectodermal cells, but that secondary mineralogical changes 
tended to obliterate, more and more, this first definite relation- 
ship (l.c. aut., p. 113, 115, etc.). Mr. Duerden entirely 
corroborates this result (Duerden, |. c. pp. 30, 34, 44, etc.). 
I also found that the unit-groups of crystalline fibres com- 
posing the skeletal lamelle showed the presence of organic 
residue, usually as minute granules and specks, and that in 
transverse sections of thick septa, the organic residue was 
quite appareut in the series of skeletal lamelle at the margins 
next the ectoderm, even atter the older lamellz had undergone 
considerable calcification changes. In some of the criticisms 
of my work by zoologists I was told I had mistaken such 
appearances, and had seen only fragments of algal filaments 
penetrating the skeleton. I had foreseen this might be said 
and purposely given drawings of coral skeletal parts pene- 
trated by filameutous algze to show that I was familiar with this 
quite different adventitious appearance. What I described 
was a persistent essential feature in every skeletal part of 
every species I examined, and now Mr. Duerden entirely 
corroborates this observation. But this is the observation 
which overturns the previous conception of the origin of the 
Madreporarian calcareous skeleton, for, as I pointed out, that 
skeleton is composed of layers primarily organic, secondarily 
inorganic, and separated successively from the polypal ecto- 
derm during the growth-periods of the polyp. 
So far, then, Mr. Duerden’s work confirms mine. But in 
