Gemmules.— Mr. Bowerbank has given the following description of the gemmules of Halichondria Johnstonia. " The gemmules of this sponge are dispersed in great abundance throughout every part of its substance ; they are of an oval form, the longest diameter being 7.-1,,th, and the shortest, the vhtli of an inch. They vary considerably in size, but the above are their averame dimensions. When seeu by direct light, wirh a power of 100 linear, they appear of the same colour as the surrounding fleshy matter ; but when viewed as transparent objects they assume an iron or slate-gray colour, having their surfaces closely studded with minute papillw, which are produced by the projection of the points of numerous very small spicula, which are imbedded in the crust or shell of the getnmule, and are dis posed in lines radiating from the centre to the circumference of the body." The form of these minute spicula is ex ceedingly various ; but the best developed ones appear conical, having their bases towards the centre of the gemmule, and their apices slightly elevating the parts of the outer in tegument immediately above them. The mode of disposition of these spicula is best observed, Iv hen a small portion of the sponge has either been treated with boiling nitric acid, or by incineration in the flame of a lamp. The dissolution of the gemmules is not effected by either of these agents, and, to view them with the greatest effect, they should be gently triturated with a little water between two pieces of glass, until some of them be broken into small pieces. In these fragments, the spicula may be seen in situ, cemented together apparently by siliceous matter, which appears to abound in the outer integument of the gemmule. Upon measuring some of these minute spicula in situ, Mr. Bowerbank found
the average length to be ,-51,z, of an inch, or about equivalent to the diameter of a disc of human blood, and their average thickness the 1-1,-1,77 of an inch, so that they are of exceed ing minuteness as compared with those found in other parts of the same sponge.
The propagation of Tethea is by means of sporules or gemmules generated within the fleshy substance. The sporules, ac cording to Dr. Johnston, resemble the parent sponge in miniature ; but they have no dis tinct rind or nucleus, being composed of simple spicula woven together by the albu minous matter ; and there seems no vvay of escape for them, except by the dissolution of the body of the parent sponge, which most probably is an annual production. " The natu ralist*, who believes that sponges have an affinity with the fungi, will see, in these par ticulars, a correspondency which may strength en his belief. The Tethea, he nnay say, is the sea's copy of the earth-born Scleroderma, and he may remind us that, like the sporules of sponges, the sporules of fungi are equally locomotive. The Chaos fungorunz of„Linnzeus is thus desciibed : — " Habitat uti semen Ly coperdi, Agariei, Boleti, Mueores, reliquorum que fungorum, in sua matre usque dum disper gatur et in aqua exclusum vivit et moritur, demum figitur, et in fungos excrescit. Zoophy torum metaphorphosis e Vegetabili in Animale fungorum, itaque contrario ex Animali in Vege tabile." — Syst. p. 1326.
The admissibility of sponges into the animal series is, indeed, extremely problematical, and we doubt not that among naturalists of the present day the balance of opinion would be unfavourable towards retaining them in the rank which they at present occupy in zoolo gical classification. _