Polystomata. 3 1 



Spicules. The skeleton of most sponges consists 

 not only of the homy material with which we are familiar 

 in the toilet sponge, but of spicules of silica of various 

 shapes embedded in the horny mass, resembling pins, 

 needles, clubs, crosses, anchors, hooks, wheels, &c. In 

 others, siliceous spicules alone make up the skeleton, 

 which has no horny matter. There is a calcareous 

 skeleton in the simple group just described. 



Reproduction and Classification. Sponges 

 multiply by division, either natural or artificial. 

 That is, if we cut up a living sponge into many small 

 pieces, each can grow into a perfect sponge. Other 

 modes of growth or reproduction are by contin- 

 uous budding, by the formation of free buds, usually 

 arising in autumn and growing in the ensuing spring, 

 or else by the formation of eggs which have been 

 found in autumn in many forms, and which develop in 

 the following year Sponges are classified according 

 to the material of the skeleton and the shapes of the 

 spicules. Thus there are calcareous, horny, and 

 siliceous sponges. The last class is the largest and 

 includes some remarkable forms, such as the boring 

 sponge (Cliona celata), which pierces holes in old 

 oyster shells on our sea-shore, and is known by its pin- 

 shaped spicules. The remarkable Neptune's cup 

 (Raphiophora) is closely allied, though very dissimilar 

 in shape and size. Hyalonema, the glass rope, from 

 Japan and Portugal, has long twisteii siliceous spicules. 

 Euplectdla, the exquisite Venus's flower-basket, from 

 the Philippines, is now well known as an ornament, 

 and exhibits a most wonderful interweaving of siliceous 

 spicules. Spongilla, the common green fresh- water 



