VI PREFACE. 



No apology is necessary for the exclusive use of the metric 

 system. If pupils lack familiarity with it, the actual handling 

 of metric measures and weights will soon remedy this. A 

 useful chart showing the units may be obtained of the Ameri- 

 can Metrological Society, 41 East Forty -ninth Street, New 

 York, for ten cents. 



Very few of the illustrations are original. In the main they 

 have been selected from a wide range of standard works with 

 especial care to secure accuracy and clearness. Whenever 

 possible the source of the figure and its magnification have 

 been given. The attention of the teacher is invited to the 

 very full description which accompanies each figure. In 

 these explanations will be found much matter which is often 

 put into subordinate paragraphs in other books. I have ob- 

 served that students are prone merely to " look at " figures, 

 and rarely study them. I therefore suggest that real study of 

 the illustrations as supplementing the text be insisted upon. 

 Sections are apt to be puzzling to beginners unless they are 

 taught how to interpret them. This can be done by requir- 

 ing them to sketch on paper or blackboard imaginary sections 

 of common objects in different planes. Articles of regular 

 form, such as a pencil, book, slate, ink bottle, desk, etc., 

 may be "sectioned," until from sketches of sections in three 

 planes at right angles the student can construct a mental 

 image of the object. 



Although divided into four parts, it has not been possible 

 to keep the subject matter of each wholly distinct, since 

 morphology, physiology and ecology are so interrelated. In- 

 deed it has been thought best to combine the morphology 

 and physiology of the reproductive organs to form Part III, 

 rather than to divide it between two. The teacher will do 

 well to see that the pupil does not neglect the abundant cross 

 references. 



While the whole book is simply a restatement of widely 



