PREFACE. 



IN the preparation of this book the author has had in 

 mind the requirements of a class of students who are 

 pursuing a course of laboratory work in Invertebrate 

 Zoology. An effort has been made to direct the work, 

 without, at the same time, actually telling the student all 

 that there is to be learned from the specimen. It is 

 taken for granted that an instructor is present to assist 

 when there is trouble, and to demonstrate many things 

 that written descriptions might only render more con- 

 fusing. 



The animals that have been selected are not always 

 the most typical, but they are generally forms that can 

 easily be secured and preserved. 



In the Appendix a few words have been given regard- 

 ing laboratory methods, etc. It has not been thought 

 advisable to introduce any considerable treatment of the 

 microscope as an optical instrument, nor have the modern 



