400 THE MICROSCOPE. 



while the spicula of some are round at one end, and 

 pointed at the other acuate ; some have spicula round at 

 one end, the former being dilated into a knob spinulate.' 



Fig. 216. 



1 Gemmnle of SpongiUa fluviatilis, enclosed in spicula. 2, Birotulate spicula, 

 ' from Flnviatilis. 3, Geinmules of SpongiUa fluviatilis, after having been im- 

 mersed in acid, to show coating of birotulate spicula. 



Among the genus Grantia, Geodia, and Levant sponge, 

 are found spicula of a large size, radiating in three direc- 

 tions triradiate. In the Levant specimen, a central 

 communicating cavity can be distinctly seen. Some 

 Smyrna sponges, and species of Geodia, have four rays 

 quadriradiate. Some spicula in P. Johmtonia and Geodia 

 have as many as ten rays multiradiate. In some species 

 of Tethya and Geodia the spicula consist of a central sphe- 

 rical body, from which short conical spines proceed- 

 stellate spicula. (Fig. 212, Nos. 4 and 5.) Spicula 

 having both extremities bent alike bicurvate have been 

 obtained from Trieste sponge. Some South Sea sponges 

 have spicula twice bent, and have extremities like the 

 flukes of an anchor bicurvate anchorate ; sometimes the 

 flukes have three pointed ends. (Fig. 212, No. 6.) The 

 gemmules in fresh-water sponges are generally found in 

 the oldest portions near the base, and each one is protected 

 by a framework of bundles of acerate spicula of the flesh, 

 as shown in fig. 212, No. 9 ; but in many marine species, 

 Geodia and Pachymatisma, they are principally confined to 

 the crust. In the fresh- water sponges, the amount of 

 animal matter in the gemmules is considerable; but in 



