vi PREFACE 



is followed in the laboratory work and two courses are offered, one carry- 

 ing a credit of ten semester hours and the other six, and differing in 

 the number of types covered. In the longer course, three recitation 

 periods a week are required; in the shorter, two. 



It is suggested that in the selection of material for a shorter course 

 the lightening of the load be done by taking in the classroom only a brief 

 survey of Chaps. XV to XVII, XXV to XXXIX, and XLI to LX, 

 inclusive, picking out sections here and there for the particular atten- 

 tion of the students and letting the rest be merely read for the general 

 impression gained. The numbering of the sections makes possible the 

 assignment of certain ones for more intensive study and of others for 

 consideration in connection with the laboratory work. 



In the topics handled in Part V, three aims have been in view: (1) 

 To give a general survey of the field of zoology with a fairly even emphasis 

 upon the various aspects; (2) to review many of the facts presented in 

 previous parts, putting them in a different setting, and developing on 

 the part of the student a broader view and a greater ability to apply 

 these facts; and (3) to establish points of attachment to which advanced 

 courses in the department may be articulated. It is felt by the author 

 that these chapters afford a means for more ready correlation between 

 the general subject and such special courses. Cross references facilitate 

 the development of the habit of thoughtful reviewing and the perception 

 of analogies and homologies, resemblances and differences, that form 

 a part of the basis for true scholarship. 



Since correct spelling and exact pronunciation are among the clearest 

 indications of careful training, the pronunciations of phylum and class 

 names are given in the body of the text and the pronunciations of words 

 in the Glossary are given. That the student may be led to observe the 

 derivations of technical terms those of the phylum and class names are 

 given and many common Greek and Latin roots are included in the Glos- 

 sary. Italics are used in the text to indicate emphasis and also to call the 

 attention of the student to words the definitions of which are to be learned. 



In the preparation of the book the author has made free use of other 

 texts and of works of reference, particularly of Parker and Haswell's 

 "Text-book of Zoology," a copy of which should be available to every 

 teacher, and of the volumes of the Cambridge Natural History Series. 

 In connection with illustrations borrowed from other books acknowledg- 

 ment is made of their sources and of the courtesy of the different pub- 

 lishers in granting permission. Of the figures, seventy-two are from 

 borrowed engravings or were reproduced photographically by F. H. 

 Shoemaker. Two of the original drawings (Figs. 108 and 115) were 

 made by S. Fred Prince. With these exceptions all of the illustrations, 

 either redrawn or original, are from drawings by the author's son, 

 Robert A. Wolcott. 



