72 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



existence, we shall next study a number of other common animals, comparing 

 them with the frog in structure, histology, and function. Just as the frog 

 forms one of a great group of animals, the vertebrates, distinguished by the posses- 

 sion of a vertebral column, so all the animals which exist upon the earth can be 

 arranged into great groups, each of which is called a phylum. There are about 

 a dozen of these phyla and they are distinguished from each other very easily 

 by large important anatomical differences. We shall study representatives of 

 several of these phyla, starting with the simplest, always comparing their anatomy 

 with that of the frog and seeing how one by one the systems of which the frog 

 is composed have come into existence. 



We trust the student has by this time been sufficiently impressed with the 

 fact that the unit of structure of the frog is the cell and that the entire frog comes 

 from one cell. We are now about to see that numerous adult animals exist 

 which consist of but a single cell, but yet are able to carry on all of the functions 

 necessary to life within the limits of this single cell. These animals belong to 

 the phylum Protozoa, or the one-celled animals. They are the simplest animals, 

 and one of the simplest among them is the one to which we shall first direct our 

 attention, the Amoeba. Read Hegner, chapter iv, pp. 37-53. 



B. THE AMOEBA 



1. General structure and locomotion. Mount a few drops of solid material 

 from the culture on a slide, cover, and examine with the low power. Cut down 

 the light. Search the slide for an irregular granular object, apparently motionless. 

 Ask the assistant whether or not you have an Amoeba or have him help you find 

 one. Study the animal with both low and high powers. Observe that the 

 Amoeba moves by putting out projections, called pseudopodia, from its surface 

 and then flowing into these projections. This type of movement is designated 

 as amoeboid movement. The protoplasm of the Amoeba may be divided into two 

 regions, an outer clear layer, the ectoplasm, entirely free from granules, and the 

 central mass, the endoplasm (also spelled " entoplasm") , filled with round or 

 dark oval granules, of unknown function, and food particles. Under the high 

 power watch the formation of a pseudopodium, and determine how the ectoplasm 

 and endoplasm behave in its formation. Does the Amoeba have anterior and 

 posterior ends or a definite form? 



Make five outline drawings of the Amoeba to show successive changes of 

 shape. Indicate by arrows the direction of flow of the protoplasm. 



2. Special structures. Find a specimen whose protoplasm is well spread 

 out and not excessively granular and look with the high power for the following 

 structures: 



a) The contractile vacuole: Watch the non-moving parts of the animal for a 

 perfectly spherical clear spot. At intervals it contracts and disappears, hence 



