176 ARTHROPODA. 



6. Four pairs of biramous thoracic appendages. What is 

 their function? 



Make a drawing of the animal. 



Wilson: The Fish Parasites of the Genus Argulus Found in the Woods Hole 

 Region. Bui. U. S. Bur. Fish., 24, 1904. 



LEPAS. (Goose Barnacle.) 



If possible, examine a cluster of specimens as they naturally 

 occur attached to floating timber. 



1. Account for the fact that the peduncles are much larger 

 in some specimens than in others. Are they contractile so the 

 body may be moved into different positions? Would such 

 movements be of value? 



2. Notice the thoracic appendages. Can they be thrust 

 from the shell? What is their character? What are their char- 

 acteristic movements? Drop a small piece of clam meat on 

 these appendages of a living specimen and see what happens. 

 What kind of food would they naturally collect? 



3. Examine the portions of the shell. The portion on the 

 closed margin is the carina, laterally and near the base of 

 the peduncle are the scuta, and near the extremity the terga. 

 Why are there so many pieces? Notice the hues of growth and 

 determine the direction of growth of each piece. 



Draw the animal as seen from one side. 

 With a scalpel or razor cut a preserved specimen into right 

 and left halves, extending the cut through the peduncle. 



4. The mouth will be seen at the end of a rather thick pro- 

 longation which extends to near the bases of the abdominal 

 appendages. On the margin of this prolongation are the small 

 scale-like mandibles, first 7naxill(je, and second maxillce. The sto- 

 mach is rather large and the small intestine leads to the posterior 

 end of the abdomen, where it opens between the abdominal 

 appendages. 



5. The nervous system, consisting of a large pair of cerebral 

 ganglia and a short ventral chain of ganglia, should be seen in 

 such a section. 



