THE SOW BUG. 71 



Is it double? How many ganglia do you count? Draw 

 a portion of the cord with its ganglia and nerves. 



11. Trace the nerve cord through the thorax. 

 Find where it passes around the oesophagus. Find 

 a ganglion above and below. 



The Live Crawfish. 



1. How does a crawfish move when swimming? 

 With what orgaa does he swim? How does he walk? 



2. How does a crawfish breathe? Where does the 

 water go into the gill chamber? Where does it come 

 out? What makes the waterflowover the gills? Put a 

 small drop of ink in the water near the hinder edge of 

 the carapace. Look for it to appear near the mouth. 



3. Does a crawfish cast off its shell? Where does 

 a crawfish live? Is there more than one kind of 

 crawfish in our vicinity? 



4. Why can a crawfish live out of water longer 

 than a fish? 



5. Where are the eggs borne? Do the young 

 crawfishes look like the old ones? 



THE SOW BUG. 



1. Locate the head, thorax, and abdomen. How 

 many segments in the thorax? In the abdomen? 



2. On the head, find the eyes. Are they stalked or 

 sessile? Simple or compound? 



3. Find the antennae. How many segments? How 

 many pairs of antennae? 



4. How many pairs of jaws? Draw one of each 

 pair. Are there palpi? 



5. Find the legs. How many pairs? Do all the 

 pairs extend in the same direction? How many seg- 

 ments in each leg? Draw. 



6. Find the gills, under the abdomen. How many? 



7. Test the shell with acid. Is there any lime in it? 



