THE PREPARATION OF MATERIAL. 279 



II. Paramecium Culture. Put a small bunch of hay into a 

 tumbler of pond water, and allow it to stand in a warm, well-lighted 

 place (not in the direct sunlight) for a few days or a week. This 

 will usually be an unfailing source of slipper animalcules. Drops of 

 water taken from the surface will be seen teeming with active minute 

 white specks visible to the unaided eye. The water of a vase in 

 which flowers have been kept too long will often furnish an abundant 

 supply. 



These creatures swim so freely, that it is often difficult to keep one 

 in the field of the microscope. If a small tuft of fine cotton fibers 

 be lowered into the drop upon the slip before it is covered, some of 

 the animals are likely to be entangled in the meshes of the cotton, 

 where they may be studied alive. The cotton also supports the cover 

 glass, so that the animals are not crushed. 



If their feeding is to be watched, finely powdered carmine or indigo 

 should also be put into the drop before it is covered. 



A method of retaining paramecium within the field for examina- 

 tion, which usually proves more satisfactory, is to mount the animal- 

 cule in a drop of gum solution made by boiling cherry, peach, or 

 plum gum in water, and diluting to the desired fluidity, and covering. 

 The gum retains the animal, restricts somewhat the action of the cilia, 

 and its refractive properties render some structures more evident. 



III. On finding Fresh-water Sponges. 1 The collector will need, 

 first of all, to know that an animal may be fixed in position, and green 

 in color. 



The sponge recommended for study in this course (Myenia fiuvia- 

 tilis) may be looked for in the clear water of ponds and lakes and 

 quietly flowing bayous. It will hardly be found in muddy water or 

 in shallow water over a mud bottom. It grows in compact or lobed 

 cushion-like masses (often several inches in diameter) upon the stones 

 of the bottom, upon " water-logged " timbers, upon boughs drooping 

 in the water, etc. It is of a yellowish or brownish or green color. It 

 may be distinguished (under a lens) from vegetable growths of 

 similar appearance by the absence in it of leaves and of long, thread- 

 like fibers, and by the presence of osteoles, of bristling spicule points, 

 and (in autumn) of gemmules. Although it is cosmopolitan in its 

 range, there do not appear to be many localities of great abundance of 

 it. It should therefore be definitely located in advance of need, so that 

 fresh specimens may be at once obtainable when needed for class use. 



1 The author has drawn largely upon the excellent monograph by Edward 

 Potts for the directions found in this and the next following sections. 



