vi PREFACE 



teacher should guide the student until the latter learns to dis- 

 tinguish important from trivial, generalized from specialized, and 

 correlated from disconnected facts. Only in this way will the 

 student learn scientific observation and inductive thought as 

 opposed to mere statement of facts and random conclusions. 

 But in order to accomplish this, the student should first of all 

 learn to observe everything that can be observed from a thor- 

 ough dissection with simple methods. 



Accordingly the treatment of the subject of this manual 

 differs somewhat from the usual. Each chapter consists of two 

 parts: a monograph in which a description is given of the animal 

 selected as representative of its class and instructions for the 

 students to follow in dissection. The descriptions while short, 

 are sufficiently detailed to include obvious structures of specific 

 value. The monographs are based partly on work done by 

 others, partly on my own dissections and investigations. To 

 these latter are due some of the divergencies from generally ac- 

 cepted opinions as well as statements not to be found elsewhere 

 in print. I have examined all important papers which have 

 been published up to the present time and if I do not give any 

 list of these it is: first, because the student has no need of them; 

 second, because the teacher will know how to get at the sources; 

 and, third, because a comprehensive list would make the book 

 too long and in consequence, too expensive, while a partial list 

 would be of no great value. 



The instructions have been followed successfully by my 

 students for two years, and have thus stood the test of the 

 laboratory. The student is expected to read the descriptive 

 part at home, the day before the exercise. The accompanying 

 figures will help him to understand the subject. At the same 

 time he will not be able to copy them in the laboratory instead 

 of making original drawings from the specimen he dissects, for 

 the simple reason that they either represent the structure of 

 some other, though nearly related species, or are diagrammatic. 

 Some of these figures are copies from other books; some are 



