42 Practical Zoology. 



or below. In fastening the appendages, first decide just where 

 the part is to lie. Then, directly under the basal part, make a 

 hole from the upper side. Then pass the thread through, from 

 below, over the appendage, and down again through the same 

 hole. The loop thus made will hold the appendage securely and 

 be little noticed if the thread has a suitable color. In this way 

 fasten each of the longer legs at three points. Leave the eyes at- 

 tached to the carapace, but arrange all the other appendages, from 

 the antennules to the last thoracic legs. Label the whole series 

 on one side, placing the name below each appendage. 



DISSECTION OF THE CRAYFISH. 



1. Place the crayfish in the dissecting pan, dorsal surface up, 

 and cover it with water. Place a double-pointed tack astride the 

 narrow part of each of the first pair of thoracic legs just back of 

 the big pinchers. By pressing strongly with the thumb the tack 

 can be set firm enough to need no hammering. Now pull the 

 body of the crayfish back taut and tack firmly through the telson. 



2. Insert the point of one blade of the scissors under the 

 hinder edge of the carapace, about an eighth of an inch to one 

 side of the middle line. Cut forward to the groove which sepa- 

 rates the head from the thorax. Break away the whole of the side 

 of the carapace. Push the gills downward, and cut them off at 

 their point of attachment. Observe the thin wall separating the 

 cavity in which the gills were, the gill chamber, from the body 

 cavity. Clear away the other side likewise. 



3. With the forceps pick away the narrow remaining strip of the 

 carapace, carefully, as the heart lies just under it. The heart is an 

 oblong, whitish body. Look for small white tubes, arteries, running 

 forward from it toward the head. How many are there? Be on 

 the lookout for other arteries. With the forceps gently lift the 

 hinder end of the heart ; note its angularity. Look for holes n 

 the dorsal surface of the heart ; how many do you find ? Look al 

 for holes on the sides and on the ventral surface. 



