400 Dr. Bovvevbauk on Hyalonema niirabilis. 



polypidom ; and it may be observed that Dr. Gray^ ia 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 

 aggregated 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 Corallidse," 

 published in the 'Philosophical Transactions of the Iloyal 

 Society,' vol. cxxvii. p. 215, I examined microscopically speci- 

 mens of a great number of corals belonging to different genera, 

 as well as many of the Gorgoniadse, but have never succeeded 

 in 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 sihceous 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) or Zoanthus. Excepting 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 polypes 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) 

 \e corium poli/pifferum enveloppe Vaxis d'une maniere uniforme, 

 il recouvre parfaitement I'une des extremites de Paxis, la plus 



