XX Introduction 



THE STEHTOR AND STYLONYCHIA 



Stentors are generally harder to develop in indoor cul- 

 tures than the common infusoria. But I have usually 

 had them present in some one of the culture jars, frequently 

 in those in which paramecia are found. Stylonychia is 

 also generally present in Paramecium cultures. 



SPONGES 



Fresh-water sponges occur as bright green growths 

 attached to stones and wood in shallow streams. The 

 shade of the green is different from anything else in the 

 environment, and together with the distinct spongy feeling 

 of the organism will enable any one to recognize it. It 

 frequently spreads over a considerable surface. 



These sponges are common in brooks, and may generally 

 be found in abundance in the little pools between the 

 large stones where the stream is rapid. They should 

 be studied fresh, as they do not bear confinement in 

 standing water very well. The gemmules occur late in 

 autumn. 



The salt-wiater sponges are common along the coast, 

 and may easily be gotten from pools when the tide is out. 

 For inland schools they may be purchased of dealers in 

 biological supplies. 



HYDRA 



, This creature has a small cylindrical body, by the base 

 of which it attaches itself to various objects in the water, 

 and from the other end of which project a number of 

 tentacles. Both the body and the tentacles are capable 

 of being expanded and contracted, so that sometimes they 



