90 On the il Glass-Rope " Hijalonema. 



however, found in connection, but are scattered along with 

 the small cross spicules (Fig. 10) in great numbers throughout 

 the whole of the sponge substance. Many spicules of the 

 awl- shaped and simple cross types, especially short spicules, 

 represented in Fig. 7, are met with within the silicious coil to 

 its very centre, and, in cases where the coil has been brought 

 home without the sponge, such needles can be shaken out 

 from the interstices of the threads. The spicules of Hy alonema 

 are marked in their character, and all the forms described above 

 are found in all specimens of the sponge imbedding the cha- 

 racteristic bundle of enormous spicules ; so that there can be 

 no reasonable doubt of the specific identity of the sponge in 

 all cases. 



Within the round apertures on the surface of the sponge 

 there is usually a brownish orange-coloured membrane. At 

 first sight one would never dream of doubting that this mem- 

 brane forms part of the sponge, but, on examining it with a 

 high power in order to make out its minute structure, Professor 

 Schultze found, to his surprise, that it presented the marked 

 characters of a polyp tissue ; in fact, that it was the remains 

 of a minute parasitic polyp, probably alcyonarian, which 

 inhabited the oscula and their passages during the life of the 

 sponge. The thread cells of the polyp membrane are quite 

 distinct, and it has even been possible to isolate entire 

 extremely minute fringed tentacles, richly clad with almost 

 linear thread- cells. 



The view adopted by Gray and Brandt, that the silicious 

 coil is the axis of a zoantharian zoophyte allied to the 

 Aiii'ipatlies, is founded upon the circumstance that the coil of 

 silicious spicules is almost always coated to a greater or less 

 extent, by a dark leathery layer, studded -with the projecting 

 bodies of true polyps. The outer surface of the investing 

 layer is rough with included particles of sand, shells of 

 foraminifera, and sponge spicules, chiefly those of Hyaloueiiia, 

 and these spicules usually become very numerous in the polyp 

 layer in the immediate neighbourhood of the body of the sponge. 

 Beneath this layer, with its contained foreign bodies, there is 

 a thick band of a nearly transparent matrix, with scattered', 

 oval, yellowish, granular masses. Within these ovals are 

 imbedded very characteristic groups of thread- cells, oval, half 

 filled with granules, and half with a delicate, spirally-coiled 

 thread. Such thread-cells are generally distributed throughout 

 tho ceenosarc, and in the walls of the polyp bodies. A third, 

 loosely-areolated, thin layer grasps closely the surface of the 

 silicious threads. Some doubt arose at first whether this third 

 layer belonged to the zoophyte or to the sponge. It most 

 likely forms the basement membrane of the ceenosarc of the 



