86 ELEMENTARY ZOOLOGY 



sometimes three. These spicules are composed of car- 

 bonate of lime and can be dissolved by pouring on to 

 them a drop of hydrochloric acid. 



Some of the sponges may have buds growing out from 

 them near the base. These buds are young sponges 

 developed asexually. If allowed to develop fully the 

 buds would have detached themselves from the parent 

 and each would have become a new sponge. 



Make drawings showing the form of a whole sponge ; 

 the appearance of the inner face of the sponge bisected 

 longitudinally; the shape of the spicules. 



A COMMERCIAL SPONGE 



TECHNICAL NOTE. For the study of the skeleton of an ocean- 

 sponge with more complex body buy several common small bath- 

 sponges without large holes running entirely through them. The 

 teacher should have also a few specimens of small marine sponges 

 preserved in alcohol or formalin. Such specimens should be part 

 of the laboratory equipment (see account of laboratory equipment, 

 p. 450), and can be readily and cheaply obtained from dealers in 

 naturalists' supplies. 



The bath-sponge or slate-sponge consists simply of the 

 hard parts or skeleton of a sponge animal. In life all of 

 the skeleton is enclosed or covered by a soft, tough mass 

 composed of layers of cells. Note the many openings on 

 the surface of the sponge. Crush a bit of the skeleton 

 and examine it under the microscope. Note that it is 

 composed of fine fibres of a tough, horny substance called 

 spongin, instead of tiny distinct calcareous spicules. 



OTHER SPONGES 



The sponges are fixed, plant-like aquatic animals. 

 The members of a single family live in fresh water, being 

 found in lakes, rivers, and canals in all parts of the world. 

 All the other sponges, and there are several thousand 

 species known, live in the ocean. They are to be found 

 at all depths, some in shallow water near the shore and 



