136 Mr. H. J. Carter on Fossil Sponge-spicules of 



forcibly with the " oozy calcareous mud " of the region in 

 which the latter live, which is also stated to be literally 

 "crammed" with their deciduous remains. 



Thus, geographically, geologically, and structurally, the 

 deep-sea sponges so differ from the Coralliospongiai that se- 

 parating them for classification becomes absolutely necessary; 

 and hence Mr. Kent, who is practically acquainted with both 

 groups, has most advisedly instituted the appropriate name of 

 Calycispongiag for the fonner (Monthly Microscojaical Journal, 

 Nov. 1870). 



The delicate though long spicules of the deep-sea sponges, 

 held together only, as before noticed, by equally delicate sarcode, 

 also contrast forcibly in structure with the rigid, silicified, 

 keratose fibre of the Coralliospongise. But if rigidity alone 

 be here considered, it may very properly be observed that in 

 this respect the long, thick, twisted spicules of which the 

 " glass rope" or stem oi Hyalonema'is, composed has no parallel 

 among any of the Spongiada?. 



Nor is it less true that this long stem, supporting a caly- 

 cifoiin sjDonge upon its upper extremity, thus prominently 

 differs from its companions Holtenia and Plieronema^ whose 

 sessile or stemless bodies are not only kept in contact with 

 the mud, but partially imbedded in it by a beard of long 

 spicules, far more delicate than those forming the stem of 

 Hyalonema. 



To this it might be added that a parasitic polype, first 

 named by Schultze Palythoa fatua (Annals, 1867, vol. xix. 

 p. 160), usually appears, according to Dr. W. Thomson's ob- 

 servation, on the stem of Hyalonema " before it is an inch 

 long, and sometimes earlier." After which we know, by the 

 specimens of the " glass rope " which are much above a foot 

 in length, that the pol}q)e not only covers the greater part 

 of them, but the upper end also, thus proving that in the 

 " struggle for life " it has caused the calycifomi head of the 

 sponge to fall off, and has thus appropriated the stem. 



Hence it becomes a matter for consideration how far the 

 difference between the stem of Hyalonema and the beard of 

 Holtenia arises from the presence of the poljq^e upon the 

 former. 



The origin of parasites is involved in obscurity, as much as 

 their modification of structure is often evident — for instance, 

 the gall on oak-trees. And as this modification is to suit their 

 own pui-poses, and the habit of a polyj^e is for the most part 

 to grow on a hard substance and live in clear water, may 

 not the Palythoa fatua have compelled the sponge, in " the 

 struggle for life," on either side, to elongate its stem, and thus 



