CHAPTER X 

 THE SPONGES (PORIFERA) 



By EDWARD POTTS,* Media, Pa. 



The zoophytes or plant animals of the old zoologists or, as they 

 are now more correctly designated, the separate groups of sponges 

 and coelenterates, are represented in the fresh waters of North 

 America through a very narrow range both of genera and species. 

 Sponges alone constitute the topic of this chapter. The student of 

 fresh-water sponges must not expect to find them resembling in ap- 

 pearance the familiar forms of commerce, which in fact are exclu- 

 sively of marine origin. Nor should he look for shapeless masses of 

 jelly; such may be found, but they are not sponges. Yet as animal 

 organisms, sponges, whether fresh-water or marine, are essentially 

 alike. Infinitely variable in form and external appearance and in 

 the character and constituents of their skeletal structure, the vital 

 parts that have clothed them, or do still clothe them if examined 

 in life, are composed alike of protoplasm or sarcode. This forms 

 the delicate tissues, structureless except when viewed through 

 powerful lenses, and builds up the inert framework whether it con- 

 sists of tough elastic fibers, as in the commercial sponge, or is the 

 fairy-like structure of flint or lime belonging to other sponges 

 foimd in the ocean, or forms skeletons, as in our fresh-water forms 

 so far as known, always of silex. The active life work of sponges 

 it is impossible to see with the naked eye and very difiicult to study 

 even under the microscope. Certain collared cells by means of 

 waving flagella feed the sponge, reject intrusive matter, and create 



* The death of Mr. Potts just after the first manuscript of the chapter had been 

 submitted laid upon me the duty of bringing it into conformity with the other chapters 

 of the book without his help. I have endeavored to do this with the least possible 

 change from the original. To make sure that no error was committed in the process 

 I secured the aid of Dr. N. Annandale, Calcutta, India, for whose kind assistance I 

 am deeply indebted. For the present form of the key Mr. Potts is in no wise responsible. 

 I am also indebted to Professor Frank Smith for valuable unpublished data in regard 

 to distribution. — Henry B. Ward. 



