400 Dr. Bowerbank on Hyalonema mirabilis. 
polypidom ; and it may be observed that Dr. Gray, in p. 292, 
himself designates the protuberances which I have termed 
oscula as “ polype-cells,” and not as polypes. I have abundant 
specimens of Corticifera, and have had several of the polype-cases 
of Zoanthus Couchii in my possession, and in all my examina- 
tions of them I could never ascertain that the polypidoms of 
either secreted siliceous spicula. These bodies, in every case 
that has come under my observation, have been formed of 
ageregated adventitious materials, principally sand, with occa- 
sionally a stray spiculum amidst the heterogeneous material 
adhering to, and incorporated in, the fleshy cases of the 
polypes. 
Dr. Gray is also mistaken in his belief that I have not paid 
sufficient attention to the structure of corals to enable me to 
escape such errors of judgment as he imputes to me; but the 
truth is, that in the course of the preparation of my paper “ On 
the Organic Tissues in the Bony Structure of the Corallidee,” 
published in the ‘Philosophical Transactions of the Royal 
Society,’ vol. exxvil. p. 215, I examined microscopically speci- 
mens of a great number of corals belonging to different genera, 
as well as many of the Gorgoniade, but have never succeeded 
im finding a single species of either of them which secreted silex 
as a material of its skeleton. Nothing was more common than 
to find a mixture of various forms of siliceous sponge-spicula 
deeply buried in the interstices of corals, and minute siliceous 
coating-sponges covering the bases and sometimes surrounding 
the stems of Gorgonias ; but in both cases such spicula were 
decidedly either adventitious or parasitical; and I think I may 
safely challenge Dr. Gray to produce a single instance of either 
a true coral or a Gorgonia secreting siliceous matter as the 
base of its skeleton, or, indeed, of any other polype-bearing 
animal the earthy base of which is siliceous. The fact of the 
presence of siliceous spicula in the inner coat of what he terms 
the bark of Hyalonema should have warned him that it could 
not belong to either of the genera “ Corticaria” (qu. Cortici- 
fera) ov Zoanthus. Hxcepting among the Protozoa, I do not 
think Dr. Gray will find a single animal which secretes silex 
in its skeleton. 
Dr. Gray writes, p. 290, that’M. Barboza du Bocage states 
that the basal portion of the axis which is inserted in the sponge 
in some of the Japanese specimens is covered with the polype- 
bearing bark, the pelypes near the base being smaller; but the 
passage quoted from M. Barboza du Bocage’s paper by no 
means bears out this assertion of Dr. Gray. The quotation is 
as follows :—‘ Chez ces derniers (les exemplaires du Portugal) 
le corium polypigerum enveloppe l’axis d’une maniére uniforme, 
il recouvre parfaitement ?une des extrémités de Vaxis, la plus 
