PRACTICAL ZOOLOGY 23 



following places : in the slime on the under side of lily 

 pads and along the stem ; in the superficial layer of mud 

 in ponds and slowly flowing streams; in damp moss 

 from sphagnum swamps ; in the deposit on the sides of 

 water barrels in greenhouses ; in aquaria which have 

 been standing for some time and which contain no crusta- 

 ceans like DapJmia, Cypris, Cyclops, etc. In case no 

 specimens are obtained from ordinary sources, amoeboid 

 cells may be used instead. These may be found by 

 tearing to pieces the gills of a clam, or a mussel, or by 

 killing a frog, cutting through the skin of the abdomen 

 or leg, and removing a drop of the colorless fluid (lymph). 

 To study the specimen, collect with a pipette a drop 

 of the water supposed to contain amoebas, or a drop of 

 lymph, place it on a glass slide, put on the cover glass, 

 and examine with a low power, f , J, or \ inch objective. 

 Be sure to have some sediment or a hair under the cover 

 glass in order that the weight of the latter may not 

 crush the specimen. 



Topics for Study. The shape, an irregular outline, 

 changing as the animal moves along (sketch the outline 

 at intervals of one or two minutes, and compare the 

 successive sketches) ; the motion, note its rate and direc- 

 tion; the change of shape is due very largely to the pro- 

 trusion of portions of the body substance in the form of 

 blunt processes called pseudopodia (singular, pseudopo- 

 dium) (Fig. I, page 57). 



With a higher power (^ or \ inch objective), examine 

 the animal's structure, noting that it is composed mainly 

 of a clear, semifluid substance, protoplasm, in which 

 are embedded numerous granular bodies of various 

 sizes and colors, some recognizable as fragments of vege- 

 table substance, together with, probably, one or more 

 diatoms or other minute organisms. In some part of 



