TKHbat fa a Sponge? 1V1 



analyze the water as it is sucked into the 

 sponge and that which issues from it through 

 the larger openings, we should find a differ- 

 ence between the two. The expelled water 

 would contain more or less carbon dioxide. 



There are many different varieties of 

 sponge, and, while they all possess certain 

 characteristics in common, they are still very 

 different in many respects. Some of them are 

 large and coarse, while others are exceedingly 

 soft and velvety. What is called a single 

 sponge is a colony of animals rather than a 

 single animal; at least they are so regarded 

 by zoologists. This can hardly be true if we 

 regard the sponge itself as a part of the ani- 

 mal. If the sponge is simply regarded as the 

 house in which the animal lives then it be- 

 comes a great tenement with numerous occu- 

 pants. But it is a tenement upon which the 

 life of the sponge depends, and is a part of it. 



The sponge could not breathe without the 

 fibrous structure in the cells containing the 

 machinery for producing the circulation. It 

 will be seen that the sponge, while it is an ani- 

 mal, is of the very simplest variety, so far as 

 its organs are concerned. True, its frame- 

 work is very complicated, but the organs for 

 sustaining the life of the animal are the sim- 

 plest possible. The little self-acting pumps 

 pull the water into the sponge through the 

 smaller openings, where it appropriates the 



