4 THE BIOLOGT OF THE CELL 



or ducks, or the gills of fishes a day or two after they 

 are caught ; by rinsing the contents of the intes- 

 tines of frogs, lobsters, crawfish, etc. Many marine 

 forms may be caught by skimming the surface of the 

 water with a net of bolting-cloth, especially on warm, 

 quiet evenings. The most practicable method of sup- 

 plying specimens for large classes is to resort to culti- 

 vations. Fresh -water forms may be raised in large 

 numbers by cutting into a dish bits of hay, grass, 

 marsh-grass, potato, fish-skin, moss, or, in fact, almost 

 any organic substance, pouring over the pieces just 

 enough lukewarm water to cover them, and setting 

 the dish, covered to prevent evaporation, in a warm, 

 not too light place for one to seven days. Another 

 very satisfactory method is to allow fresh-water weeds 

 and algas to decay in a small amount of water. Many 

 marine forms may be cultivated by soaking in artificial 

 sea-water for a few days bits of oysters, clams, and the 

 gills of unboiled lobsters. As particular forms usually 

 have definite habitats, it is best not to obtain all of the 

 specimens from a single locality, but to gather them 

 from as various sources as possible. In the cultivations 

 some forms will be found at the edge of the dish at the 

 surface, others on the bottom, others attached to the 

 sides, some swimming freely, and still others fastened 

 to the pieces of organic material. 



To study the specimens properly the student will 

 need the following apparatus : A compound microscope 

 magnifying from fifty to four hundred diameters, slides 

 and cover-glasses, and a pipette. 



Method of Examination. — Take a clean glass slide, 

 with the pipette put in the centre of the slide a drop of 

 water thought to contain specimens, lay a piece of hair 



