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REPORT ON ZOOLOGY, MDCCCXLII : 
throw out small excremential grains. The cause of the circulation of 
water through them he could not discover ; hut he is convinced, that 
it does not originate from any insect accidentally concealed and breathing 
in the sponge, as Hogg some time since asserted (Ann. Nat. Hist. vi. 
p. 316; Transact, of Linn. Soc. vol. xviii. p. 363; Trans. Ent. Soc. vol. 
iii. p. 105). 
Johnston has sometimes found oval corpuscules in Tethea and Hali- 
chondria, which were composed of a gelatinous substance, with numerous 
spicula imbedded in it ; but he supposes they are not eggs, since they 
did not at all agree with those ciliated eggs which Grant had discovered 
in several species, and which have been again mentioned by Laurent 
(ITnstit. 1841, p. 242). 
Johnston assumes, that the sponges increase by a sort of self-division, 
small particles detaching themselves from the gelatinous fluid, and de- 
veloping into their species, after they have become fixed on an appro- 
priate site. 
Sponges consist of a loose, elastic, fibrous, or porous substance, in which 
spicula are often imbedded. Besides the numerous pores, stiU larger 
openings are found on difierent spots of the surface, from which canals 
pass, in the most various directions, through their substance. The fibres 
in the proper sponges are cylindrical, of unequal thickness, and reticu- 
larly united together; in Tethea, Halichondria, and Spongilla, there 
are siliceous spicula in this fibrous web, and in Grantia calcareous ones. 
Johnston divides the British Sponges into eight genera: — Tethea, with 
two species, T. cranium and lyncurium ; Halichondria, with thirty- 
six species, two of which are new ; Spongilla, with two species, the 
fiuviatilis and lacustris ; Spongia, with three, limhata, pulchella, and 
laevigata ; Grantia, with eight species ; Duseideia has two, fragilis and 
papillosa; Halisarca, of which the only species is H. Dujardinii ; 
Geodia, G. zetlandica ; and Pachymatisma, also with a single species, 
P. Johnstonii. 
He next compares the different views of Naturalists respecting the 
Lithophytes, which are sometimes reckoned with the vegetable, some- 
times with the animal kingdom. He coincides with those who believe 
them to be vegetables, since they are formed quite difierently from the 
zoophytes, and bear no polypi. The British Lithophytes form two 
families ; Corallinece, of vegetable form, branchy and articulated ; and 
Nulliporidce. Of the former are mentioned Corallina, with three 
species ; Jania, with two species ; and Halimeda, with one species. Of 
the latter, Nullipora is the sole genus, with four species. 
Bowerbank has examined a keratose sponge from Australia (Ann. 
Nat. Hist. vii. p. 129). He found siliceous spicula, of various shapes, 
imbedded between the horny fibres, and here and there groups of round 
bodies, which he did not know whether to consider as gemmules or eggs, 
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