PRINCIPLES OF ANIMAL BIOLOGY 9 



drop of erythrosin, which is a staining solution. After half a minute 

 remove the surplus stain, add a drop of distilled water, and put on a 

 cover-glass. Which part of the cell is most intensely stained? 



Draw a group of three or four cells, each one about half an inch in 

 diameter. An outline of the cells and their nuclei will suffice, but it 

 should be neat. Label nuclei and cytoplasm. 



16. Examine a section of the liver of a frog or salamander which 

 you will find in the tray on the table. Is this made up of cells? What 

 part of the cell is most intensely stained? Is a nucleus found in each 

 cell? If not, explain its apparent absence. 



Ic. Examine a slide of stained snake, bird, or salamander blood. 

 Draw an oval corpuscle in outline, showing the nucleus. This is one 

 of the corpuscles which gives the blood its red color but its present red 

 color is due to the fact that it has been stained. 



Id. From a culture containing Protozoa (one-celled organisms) 

 mount a drop of water. Before putting on the cover-glass, examine the 

 slide with low power to see that the organisms are present. Then add 

 a drop of acetic methyl-green, mixing the stain with the drop containing 

 Protozoa, and put on the cover-glass. 



This solution kills the organisms and stains the nucleus of each. How 

 many kinds of nucleated organisms do you find? 



In the cells studied thus far the nucleus, cytoplasm and cell membrane 

 have been demonstrated. During the remainder of this study note 

 carefully whether these cell structures are present in the cells studied. 



2. What are Some Other Structures Found in Cells? 



2a. Examine a leaf from the growing tip of Elodea. Note the cell 

 wall which limits the protoplasm of the cell. Is this cell wall relatively 

 thick or thin? Draw the cell wall of a single cell showing also the con- 

 nections with the walls of neighboring cells. The figure should be 1J 

 to 2 inches long. 



Do all cells have enveloping structures such as cell walls or cell mem- 

 branes? Reserve the answer to this question until you have examined 

 the cells in the remainder of this study and include your answer, which 

 should be in some detail, in the summary. 



26. Examine Euglena or other green flagellate for colored bodies. 

 Mount in water a bright green leaf of Elodea taken from a growing tip 

 of a branch and examine it for colored bodies. These are plastids. 

 Search in Elodea for plastids shaped like two biscuits fastened together. 

 How do you explain this shape? Color of fruits and of many flowers may 

 be due wholly or in part to the presence of colored plastids. Chromo- 

 plast is a general name for all colored plastids while the word chloroplast 

 is used to designate only green plastids. 



Draw in outline one cell with its plastids. If Elodea is chosen for 



