44 Practical Zoology. 



11. Draw the point of a knife blade or dissecting needle along 

 the middle line of this muscle, at the bottom of the groove in 

 which the intestine lay. After a thin layer has been cut through, 

 the whole muscle may be easily separated into two rolls the whole 

 length of the abdomen. Roll these carefully aside, pushing 

 equally right and left; otherwise the nerve cord may be. injured. 

 Find in the middle line of the floor of the abdomen a slender 

 white nerve cord, with enlargements at intervals. How many of 

 these enlargements, ganglions, are there in the abdomen? What 

 relation do the ganglions have to the segments? Observe the 

 branches, nerves, given off to the- muscles on each side. Trace 

 the nerve cord forward to the thorax, where it disappears in the 

 hard framework of the floor of the thorax. Break away as much 

 of this framework as is necessary to follow the cord to the head. 

 Make out that the cord is double. How many ganglions are 

 there in the thorax? Note the branches extending to the legs 

 and other organs. From the large ganglion back of the gullet 

 trace two branches forward, one on each side of the gullet, till 

 they unite in a large ganglion above the gullet, thus forming the 

 esophageal collar. From the ganglion above the gullet trace nerves 

 to the eyes, antennae, and antennules. 



12. Cut open the stomach, wash it out with water, and look on 

 its inner walls for teeth. 



13. Below and in front of the stomach, find a pair of pale green 

 bodies. These are the kidneys or " green glands." Remove the 

 stomach and study the structure of the kidneys. Find where they 

 open externally. 



14. Study the joint in one of the big pinchers. Pick out the 

 muscle from the end of the segment, and find the thin, tough 

 white tendons. Seize these with the forceps and pull alternately, 

 to see how the claw .is shut and opened. Which is larger, the 

 muscle that opens the claw, or the one that shuts it ? Explain. 



15. In what characters is the crayfish like the grasshopper? 

 In what do these animals differ? Make a concise list of the 

 points of likeness and difference. 



