100 THE SEA SHORE 



The object to be dissected is placed in the trough, secured in 

 position by means of a few ordinary pins, and then completely 

 covered with water. 



We need hardly impress upon the reader the great importance 

 of thoroughly examining all external characters all those structures 

 that are visible without actual dissection before attempting to 

 remove anything ; and we have already insisted on the importance 

 of carefully examining all creatures while alive before anything 

 else is done. The value of this latter stipulation can hardly be 

 overestimated, for in many instances it is almost impossible to 

 detect the use of an organ unless it has been observed in action ; 

 and the enthusiastic student will go even further than this, for he 

 will make it an invariable rule to sketch everything he sees, and to 

 make full notes on all his observations. 



When pins are used to fix the object under examination and it 

 is generally essential that the object be fixed their heads should 

 be turned outwards ; for then the object will not slip from its 

 position, nor will the pins tend to get in the way of the work. 



Some objects are of such a nature that they are not easily 

 secured by means of pins, and yet require to be fixed in some way 

 or other. Thus, one may desire to examine the structure and 

 appendages of a prawn or small crab, or to investigate the nature 

 of a chiton. In such instances as these it is a good plan to make a 

 cake of paraffin wax of suitable size by pouring the melted substance 

 into a mould, then secure the object in proper position in the wax 

 while still fluid, and pin the latter to the cork of the dissecting trough. 



It is often necessary to trace the courses of internal passages 

 that open on the surface of the body, or of tubes that are revealed 

 during the progress of dissection, and this may be done by means 

 of a little instrument called a seeker. It is simply a blunted needle, 

 bent into a large angle, and mounted in a handle ; or, it may 

 consist of nothing but a moderately long and stiff bristle, rendered 

 blunt at one end by tipping it with melted sealing wax. This is 

 not always sufficient, however, for it frequently happens that 

 certain tubes and passages in animal forms are disposed in such a 

 complicated manner that it is impossible to send even the most 

 flexible seeker through them. For instance, suppose one desires 

 to trace the course of the digestive tube of some large bivalve 

 mollusc with its many reflections, the seeker is useless except that 

 it will penetrate to the first sharp bend. The arrangement of such 

 a tube must be traced by dissecting along its course, but this may 



