o PREFACE. 



which the instruments should be held, etc., or to point 

 out all the numerous possible mistakes which may be 

 made. It is better to leave something to the intelli- 

 gence and discretion of the teacher or the pupil, if the 

 dissecting is to prove a healthy discipline. 



It is but proper to say that the general idea of the 

 arrangement of the directions for dissection was taken 

 from the very excellent book on " Practical Zoology" 

 by Marshall and Hurst. 



I take pleasure also in expressing my thanks to my 

 friend Mr. T. D. Coleman, Assistant in Physiology in 

 this laboratory, for his kindness in helping me in the 

 dissections and in the preparation of the diagrams. 



W. H. Howell. 



Johns Hopkins University, 

 Baltimore, Md. 



