764 THE LIVING ANIMALS OF THE WORLD 



CHAPTER VII 



SPONGES AND ANIMALCULES 



THE Sponges are regarded as a group standing on the border- 

 land between the Polyps and the lowly organisms which 

 follow. The familiar Bath- and ToiLET-SPONGES of com- 

 merce represent but an insignificant fraction in comparison with the 

 many hundred species which find no place in the world's market. 

 Toilet-sponges owe their intrinsic value to the relative fineness and 

 elasticity of their component fibrous skeletons. In these particular 

 species the skeleton is composed of a substance akin to horn. In 

 • other sponges the skeleton may consist of horny fibres mixed with 

 flinty spicules, or it may be of flint only, or of spicules of carbonate of 

 lime. Finally, there are sponges which possess no internally support- 

 ing skeleton, fibrous or spicular, and whose substance is consequently 

 little more than gelatinous. All these numerous forms, however, 

 agree with one another in the identity of their most essential vital 

 elements. In the living sponge the skeleton, fibrous or otherwise, 

 is embedded within a gelatinous matrix by whose component cells 

 it is excreted. Externally the sponge-body is perforated over the 

 greater portion of its extent 

 by minute holes or pores, 

 while one or more holes of 

 relatively large size occupy 

 the summit of the sponge, 

 or are scattered here and 

 there among the numerous 

 smaller pores. The smaller 

 pores represent incurrent ap- 

 ertures, and lead to chambers 

 within the sponge's substance 

 lined by cells. Each of these 

 is provided with a long whip- 

 like appendage, with a trans- 

 parent wineglass-shaped cup 



or collar, which is a beautifully constructed food-trap. 



The lashings of the whips of the collar-cells cause 



currents of water bearing nutrient particles to flow in 



at all the smaller pores. Arriving at the chambers, 



these particles are caught by the outstretched collar-traps 



and absorbed into the cell's substance. The water, 



together with rejected and waste materials given off by 



the sponge-body, is carried forward, and passes out at the 



larger orifices or vents. 



Among the more remarkable sponges may be men- 

 tioned the Neptune's-cup Sponge, like a huge chalice 



3 or 4 feet high, indigenous to the South Seas; the 



wonderful cornucopia-shaped Lace-SPONGE, consisting of 



a lace-like reticulation of flinty fibres; and its near 



ally the Glass-rope Sponge, forming a cup- or bird's- 



nest-shaped body, supported on a long cylindrical stalk 



Fholoh H^. Savilh-Kenl, F.Z.S., 

 Milford-cn.Sta 



FRILLED sponge 



A specUs not infrequently dredged 



up by the pearl-shell fishers in 



Sharks^ Bay, Western 



Australia 



Fhslt by H^. Savillt-Ktnl, F.Z.S,, Milford-aa-Sea 



RETICULATED SPONGE 



TAe skeleton of this sponge is composed of fine 



horny fibres resembling those of ordinary 



commercial sponges 



