334 Mr. H. J. Carter on the Ultimate 
above mentioned, but with this difference, viz. that the sponge- 
cells are double the size of those in [sodictya and the siliceous 
sponges—that is, about 1-3000th of an inch in diameter. 
Thus it is proved that the ampullaceous sac is the eating- 
organ in Spongilla and in the marine sponges, both calcareous 
and siliceous, generally. 
ave alluded to the * investing membrane," or veil of sar- 
it in the Geodidee (Spherospongia, Gray) to my illustrations 
of Pachymatisma Johnstonia (Annals, vol. iv. 
loped in this respect} that the crust and the zone of triradiate 
spicules generally come away together, and cannot be sepa- 
rated without much injury to the former. 
