INTRODUCTION. 



The following pages contain a brief summary of the methods 

 ordinarily employed in the dissection and microscopical 

 examination of animals. They are not intended to form an 

 exhaustive account of anatomical technology ; and in many 

 cases they are repetitions of the practical directions given in 

 other parts of the book. 



I. ON THE OBSEBVATION OF ANIMALS DUBING LIFE. 



All animals should be carefully observed alive before they 

 are dissected, for by this means alone is it possible to obtain 

 a clear idea of the uses and mode of action of many organs, 

 such as the tentacles of Hydra, the odontophore of a snaU, 

 the scaphognathite of a crayfish, etc. 



II. ON DBAWING. 



Careful drawings must always be made, both of the living 

 animal and of all dissections and preparations. These draw- 

 ings should be made to scale, in a book kept for the purpose,, 

 and on one side of the page only. 



Correctness of outline is of more importance than minute 

 detail ; and the usefulness of the drawings is greatly increased 

 by the systematic use of diagrammatic colouring. A separate 

 colour should be employed for each system of organs, the- 

 several parts of which may be indicated by gradations of tint- 

 As a rule, the more bulky organs, as the liver, should be 

 coloured with dull tints, and the brighter colours reserved for 

 the smaller and less conspicuous parts. Arteries are usually 

 coloured red, and veins blue. 



