the Greensand comjpared with those of existing Species, 137 



reciprocally to produce the modifications which cause it so to 

 differ from the beard of its companions Iloltenia and Phe- 

 ronema, which have no parasite? In short, might not the 

 stem of Hyalonema have been the same as the beard of Ilol- 

 tenia, had not the former been accompanied by a parasite ? If 

 so, then Dr. Gray's separating the sponge at the top from it, 

 and giving it another name {Carteria) is joerfectly reconcilable; 

 for the stem would then be a joint production of Hyalonema 

 Sieholdii, Grray, and Carteria^ Gray, with the latter name for 

 the sponge alone, — thus retaining in Hyalonema Sieholdi, as 

 Schultze has very properly observed, the name of the cele- 

 brated Japanese traveller who, so far as we know, sent the 

 first specimens to Em-ope (Annals, I. c). 



There are other sponges which have a parasitic polype on 

 them besides Hyalonema. Thus, Schmidt (Adriat. Spong. 

 1862, Taf. 6. figs. 2 & 3) gives figm'es of two Halichondi'oid, 

 erect, branching species, viz. Axinella damicornis and A. ver- 

 rucosa, each characterized by pin-like and acuate spicules, and 

 on each of which there is a social parasitic polype imbedded 

 in its proper cortical layer. But in the British Museum there 

 are several specimens of a fiat Halichondroid amorphous 

 sponge (^e?ie*eyrt?), whose reticular fibre is charged with small 

 acerate and slightly cmwed spicules, and on whose upper 

 surface are plentifully scattered solitary polype-heads about 

 1-1 2th of an inch in diameter (in the dried state). These, 

 which have been likened by Dr. Gray to the parasitic genus 

 Bergia of Michelotti (P. Z. S. 1 867, pp. 239 & 514) , are imbedded 

 alone, that is, without cortical layer, in the surface of the sponge. 

 Their disks are charged with sand and deciduous spicules, entire 

 and fragmentary, of different kinds ; and so far, with their other 

 polype-structure, they differ from the sponge in which they 

 are imbedded ; but beyond this they are directly continuous 

 with the sti-ucture of tlie sponge, which thus evidently serves 

 the pui-pose of a cortical layer or coenosarc, and so stands in 

 relation to them as the root-stock of a fruit-tree to its graft, 

 there being as much difference between them and the sponge 

 as between the insect which forces the oak to supply the 

 " gall " and the oak-tree itself, so far as separate organization 

 goes. What the modifications of tlie sponge-structure imme- 

 diately around the polype-head may be, I am not prepared to 

 state ; but it is reasonable to infer that these are such as would 

 not have been there, had the polype-head not been present : 

 hence the Palythoa fatua with its social polypes and cortical 

 layer may make use of the sponge-stem of Hyalonema, and 

 thus, to meet the circumstances of the case, occasion the mo- 

 difications in it above mentioned. 



Ann. & Mag. N. Hist. Ser. 4. IW. vii. 10 



