62 LABORATORY STUDIES IN ZOOLOGY 



Study the formation of a pseudo podium. The first indication 

 of its appearance is a bulging of the ectoplasm. This is followed 

 by a current of endoplasm into the extended ectoplasm. Because 

 these extensions form only a temporary means of locomotion 

 they have been given the name "pseudopodia." These tempo- 

 rary organs appear capable of extending from any part of the 

 surface. 



Make a number (five or six) of one and one -half inch outline 

 drawings of the amoeba at intervals of a minute or more, to show 

 successive changes of shape. By arrows indicate the direction 

 in which the protoplasm is flowing in different parts of the animal, 

 at the time the figures are drawn. 



Study the structure of a favorable specimen (one whose proto- 

 plasm is not too granular) and look for the following features, 

 using the high power. 



1. Bear in mind that this is a unicellular organism. It is 

 composed of cytoplasm as the main mass, within which one or 

 more granular nuclei can often be seen in the living specimen. 

 If the nucleus is not visible in the active specimen study stained 

 preparations. Before considering the structure of an amoeba 

 it will be of advantage to have in mind one of the chief differences 

 between this single-celled animal and a single tissue cell or a 

 fertilized egg (zygote) from which all multicellular animals arise. 

 The single-celled amoeba is independent of all other cells, while 

 a tissue cell is dependent upon others in the association, and a 

 fertilized egg cannot exist indefinitely without dividing into a 

 number of cells, thus forming an interdependent and interacting 

 association of cells. 



2. Search the non-moving part of the endoplasm for a spherical 

 clear spot. At intervals it contracts and disappears to reappear 

 later and does so with more or less rhythm. Because of its 

 nature and behavior it is called the contractile vacuole. Observe 

 several pulsations and estimate the frequency. The contractile 

 vacuole is a space so fashioned and functioning as to eliminate 

 liquids from the interior of the cell. 



3. The endoplasm also contains particles of ingested food 

 the larger of which are surrounded by a fluid and hence are 

 called food vacuoles. Other cell inclusions may be found such as 

 oil droplets, crystals, and perhaps foreign particles. 



If possible find a specimen which is taking in food and watch 

 the procedure. Observe the method of passing an object with 



