GENERAL INTRODUCTION. 5 



mark the scale adopted, as, e.g., X 2 when the draw- 

 ing represents the object twice its size. 



The outlines should first be traced very lightly 

 with a soft pencil, so that they may be readily 

 altered. When the sketch is complete the outlines 

 may be gone over with a harder pencil or with ink, 

 and the different parts may be made more distinct 

 by slightly shading them with colored crayons. 



Outlines should not be sketched in color. Certain 

 colors should be used for special organs or tissues. 



PRELIMINARY PRACTICE WITH THE MICROSCOPE. 



I. Scales from the wing of a butterfly. 



Take with a scalpel some of the colored parti- 

 cles from the wing, place them upon a slide 

 and examine with AA 2, Compare the ob- 

 ject as it appears when illuminated by the 

 the mirror (" transmitted light"), and when 

 the light from below is cut off ("reflected 

 light"). Examine successively with AA 4, 

 D 2, D 4, and make a series of outline 

 sketches of a few of the scales to show the 

 difference in magnifying power. 

 II. Put a few fibres of wool into a drop of water 

 upon a slide. Put on a cover-glass and 

 examine first with a low and then with a high 

 power. Note the form of the fibre by care- 

 fully focussing at different levels. Sketch 

 CD 2). 



