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 Spongilla fluviatilis, enclosed in. spicula. 2, Birotulate spicula, 

 'from Fluviatilis. 3, Gemmules of Spongilla fluviatilis, after having been im- 

 mersed in acid, to show coating of birotulate spicula. 



Among tbe 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 



