SYSTEMATIC ZOOLOGY FOR TEACHERS, 



259 



with the unaided eye. Fresh water sponges may be found common in slug- 

 gishly flowing streams and in ponds and ditches. 



General Conclusions. 



We find that a sponge is an animal with several sets of similar organ- 

 isms, which are probably controlled by nervous force and which act in har- 

 monious concert in certain emergencies, just as the organisms of higher ani- 

 mals act under like circumstances. Although reproduction is sometimes ac- 

 complished by buds, the young are mainiy derived from fertilized ova .• 

 consequently the sponge is a metazoan: 



Fig. 126. 





\ . wlf. .S~ !'''<<* 



■ : ; / i 





.1} ,. ^s^/^\ 



/, 



asm*. 



Ydung Tube Sponge* 



Points of Advancement. 



In sponges we find a number of points of advancement over the single 

 C2lled animals. The first, and perhaps the most note worthy fact is, that 

 there are a number of cells combined together to constitute one individual. 

 The cells so congregated have become differentiated to perform different func- 

 tions. Among these functions are primarally the reproductive organs, male 

 and female, all set apart for the propagation of the race. 



