Fresh-Water Sponges 



165 



All sponges are aquatic, and most of them are marine. 

 Only the fresh-water forms produce statcblasts, and 

 live as annuals. 



In figure 74 we show two other simple metazoans 

 (unrelated to Hydra and of higher structural rank 



FIG. 75. A semi-columnar sponge from the Pulton Chain of Lakes near Old 

 Forge, N. Y. Half natural size. Photo, kindly loaned by Dr. E. P. Felt 

 of the N. Y. State Museum. 



than the sponges) that during the history of syste- 

 matic zoology, have been much bandied about among 

 the groups, seeking proper taxonomic associates. 

 Chcetonotus often appears on the side of an aquarium jar 

 gliding slowly over the surface of the glass as a minute 

 oblong white speck. It is an inhabitant of water con- 

 taining plant infusions, and an associate of Paramecium 

 which to the naked eye it somewhat resembles. 



