36 



HARDWICKE'S SCIEN CE-GO S S IP. 



tbe bark evidently extends between- and invests 

 each of tbe fibres of the rope-like axis, 



Dr.Gray's description is exact so far as the external 

 appearance of the sponge is concerned, but his 

 surmise that the so-called spongy base is a distinct 

 organism, recent observations have proved to be in- 

 correct. This basal portion is an integral portion 

 of the sponge, and, when growing, is uppermost, the 



il 



rig. 20. 



IB^ 



Fig. 19. hyalonema mirabilis, 5 nat. size. 



Fig. 21. 



long fibres being buried in the ooze, as in tlie allied 

 forms Fharonema {Holtenia) Carpenteri and P. 

 Grayi, (See Monthly Microscopic Journal, vol. iii., 

 for a most interesting paper on theseand other nearly 

 allied forms, by W. S. Kent, T.Z.S., F.RM.S.) 



The earliest known specimens of this sponge 

 were from Japan, but witliin the last few years 

 other habitats have been discovered. Professor 

 Perceval Wright found it in situ in Sctubal, off the 

 coast of Portugal, in 18G8, obtaining many Cue 



specimens from that locality, and had the oppor- 

 tunity of examining them whilst alive. He states 

 that the siliceous stem is truly a part of the sponge- 

 mass, and that the "Polythoa" (bark) was simply 

 parasitic upon the stem. Some of the Setubal 

 specimens were very large, the stems of several 

 measuring nearly two feet in length, and the head 

 consisting of a somewhat oval mass, about eight 

 inches in the long and four inches in the short 

 diameter. On opening out the sponge, the interior 

 concave surface was found to be lined with a 

 delicate network of spicules and sarcode ; a number 

 of large openings {oscula) were also seen, and these 

 were covered with a network of sarcode, the edges 

 of the meshes thickly covered with spicules, called 

 by Dr. Bowerbank " spiculate cruciform spicules " 

 (fig. 28). The professor then goes on to say that 

 he " has seen the parasitic Polythoa in a living state 

 on the siliceous axis of the Hyalonema, and that 

 he watched the polyps expand their tentacles, after 

 the fashion of any other zoautharian, to prove that, 

 though they have mouths, these mouths are their 

 own, and not at the service, directly or indirectly, 

 of the Hyalonema." Dr. Bowerbank is, liow- 

 ever, of opinion that the Polythoa is a portion 

 of the sponge, and not parasitic. The evidences 

 in favour of the latter supposition are (at least 

 so far as I have been able to ascertain), firstly, 

 that the Glass-rope has never been found without 

 the "bark;" secondly, the spicules are siliceous 

 (in all other spicule-beariug species of Polythoa 

 they are calcareous) ; and that some of them are 

 common to every portion of the sponge ; neither 

 am I aware that the Polythoa has ever been found 

 investing any other organism. 



The spicules in this sponge are perhaps more 

 beautiful and varied than in any other sponge 

 hitherto discovered. In describing these forms I have 

 adopted the terminology used by Dr. Bowerbank 

 in his work on the British Spongiadce. 



Pig. 19 represents the sponge slightly reduced in 

 sizo. 



Pig. 20. — A portion of one of the fibres, auchoriug- 

 spicules, of the " Glass-rope," showing its lami- 

 nated structure, and a transverse section of same, 

 showing mode of growth. The primary fibre is in- 

 vested with the sarcodous material : this secretes a 

 siliceous casing, which again becomes covered with 

 sarcode, the process being indefinitely repeated ; 

 X 400, 



Pig. 21. — Bi-clavatc, cylindrical, the shaft slightly 

 curved, attenuated below ; the obtuse spiculate 

 ends gradually increasing towards the somewhat 

 turgid centre ; common in the coriaceous envelope 

 (Polythoa); x 200, 



Pig. 22.— Attenuated rcctangulated hcxradiate 

 spicule, common in all parts of the sponge ; x 200. 



Pig. 23. — Cylindro-cruciform, shafts smooth, the 

 ends spiculate ; x 200. 



