134 



THE ANIMALS AND MAN 



a meter (39 in.) in height. In color they may be red, 



purple, orange, gray, and sometimes blue. 



Examine a bath sponge and note the holes in it. These 



are to let in and out the sea- 

 water, in which float the minute 

 bits of animal or plant sub- 

 stance on which the sponge 

 feeds. This water also brings 

 oxygen for the breathing of 

 the sponge, and carries away 

 the carbon dioxide given off 

 by it. But the sponge has no 

 special organs, its soft flesh 

 being able to digest food and 

 take up oxygen without stom- 

 ach or lungs. 



The living sponges are col- 

 lected by divers, or are dragged 

 up by men in boats with long- 

 poled hooks or dredges. 



They are first killed by 

 exposure to the air, and then 

 thrown into tanks of water. 

 Here the flesh decays away, 

 leaving the tough, horny, or 

 leathery skeleton, which, when 

 cleaned, bleached, and trim- 



FIG. 54. The skeleton of a glass med j g read ^ m ^ rkeL 

 sponge, composed of siliceous J 



spicuies; from Japan. (Natu- Some sponges have a lime and 

 ral size -) some a glass skeleton instead 



of a horny one, and the glass skeletons are often very 



beautiful (see fig. 54). All the sponges compose the animal 



branch called Porifera. 



Hydra. One of the most interesting of the simple animals 



found in fresh-water ponds is Hydra (fig. 55). Though 



