REMARKS TO THE STUDENT 



XXV 



clear that we are showing one object that is above another. How 

 necessary it is to have the lower object disappear sharply behind the 

 upper one will be seen if the reader will take a pencil and prolong one 

 or more lines of the lower rectangle slightly within the border of the 

 upper one in Fig. 2 C. As in Fig. 1 F, we may modify Fig. 2 C to 

 present the appearance of the two cylinders shown in Fig. 2 D. 



The necessity of showing one object over another occurs in every 

 biological drawing of any complexity that attempts to represent a third 

 dimension. The principle of such representation is simple, and its 

 application can be easily mastered. For example, a loop of an intes- 

 tine would be represented as in Fig. 2 E. The relationships of two 

 neighboring blood vessels might be shown as in 2 F. Again, part of a 

 sphere appears as in Fig. 3 A when seen from a straight side view; 



Fig. 3. — Use of lines, as in Fig. 2, to show dome-shaped bodies. 



but 3 B looks more like such an object. The representation of an 

 umbrella in 3 C, and that of a jellyfish in 3 D, apply this principle in 

 the representation of familiar objects. In these last two cases the 

 distance of the parts on the far side is suggested further by fainter 

 lines. By these simple methods, drawings on a flat surface are made 

 to express the third dimension, that is, to give the impression of depth 

 seen in the real object. 



What has been said above applies to line drawings or those in 

 which no shadows are indicated. It is surprising how much can be 

 shown by lines alone, as in the accompanying Fig. 4, in which the 

 careful drawing of the posterior end of the body gives a remarkable 

 suggestion of distance. The line drawing is the foundation for all 

 biological figures of the sort under consideration. You should learn 

 first to make good line drawings. In some laboratories these alone 



