904 DR. BOWERBANK ON HYALONEMA LUSITANICUM. [NoV. 28, 



to reiterate his belief that " Hyalonema is a type of a peculiar family 

 of Corals, formed by zoanthoid polypes, characterized by forming for 

 their support a siliceous axis formed of many thread-like spicules 

 coiled together into a rope-like form, each formed of numerous con- 

 centric laminae, and surrounded and separated from one another by 

 the corium of the community of polypes." I should not have 

 noticed this reassertion of his opinions if he had not endeavoured to 

 establish certain laws which are in themselves essentially false, and 

 on which he bases his reasonings in favour of his own theory. In 

 the first of these Dr. Gray asserts, " Silica is not exclusively secreted 

 by sponges, as the advocates of the sponge-theory seem to believe, 

 but is found mixed with corneous matter (as it is mixed in Hyalo- 

 nema and Eupleetella) in Gorgonia and Antipathes, and with calca- 

 reous matter in Madrepores." 



In the first place, no one, to my knowledge, has ever asserted that 

 silica is exclusively secreted by sponges ; nor is the silica to be ob- 

 tained from Corals and Gorgonias in the same state as it is in Hya- 

 lonema and Eupleetella, In the former two it has never been dis- 

 covered in an organized condition, while in the latter two it is always 

 in that state. 



Dr. Gray quotes the analysis by Mr. Children of Gorgonia fiahel- 

 lum, in which he found silica enough to form " a globule before the 

 blowpipe;" and the Doctor says, "This proves that silica is found 

 in the coral of Alcyonaria or polypes with pinnate tentacles." 



But the results of this analysis by Mr. Children do not bear 

 efi^ectively on the point in dispute, which is whether polype-bearing 

 animals secrete silex as well as carbonate of lime in an organized 

 form as portions of their bony skeletons. There is no doubt that 

 corals, Gorgonias, and zoophytes living in waters continually charged 

 with minute grains of sand and with silex in solution would receive 

 and retain within their fine pores numerous grains of that substance 

 which would only be liberated and recognized by the chemical disso- 

 lution of those bodies. But this adventitious acquisition of silex by 

 creatures whose organic structures are essentially calcareous is no 

 proof of their power to secrete and organize silex as well as carbo- 

 nate of lime ; and Dr. Gray does not produce a single example of any 

 polypiferous animal, either among the bony corals, the Gorgoniadse, 

 or zoophytes, secrethig and organizing silex as part of their skeleton- 

 structure. The difficulty of the purely siliceous structure of all parts 

 of the skeleton and internal siliceous organs of Hyalonema, con- 

 sidered by Dr. Gray a coral, still remains to' be solved by him; 

 and among all the beautiful siliceous organized forms so famihar to 

 microscopists of the present day there is not one that can be assigned 

 to any polype-bearing animal, described or undescribed ; and I be- 

 lieve that the animal power of organizing sihceous matter to form 

 either an internal or an external skeleton will be found to be strictly 

 confined to the great subkingdom of the Protozoa. 



The second law that Dr. Gray enunciates is, " The structure of 

 the siliceous spicules of sponges is very similar to, almost identical 

 with, the structure of the axis of Gorgonia among the sclerobasic 



