A MANUAL OF ZOOLOGY 27 



gan and the membrane Isthe tympanum. The next seven or 

 eight segments are very similar and without appendages. 

 Note the spiracle or breathing pore on each. Also note 

 the sterna and the pleura and how the two are united 

 by a thin membrane. In the female specimen note the 

 ovipositor consisting of four strong, curved, and pointed 

 pieces which form the most caudal part of the body. How, 

 and where does -the locust lay its eggs? \y;hat sugges- 

 tion do you get from the structure of the ovipositor? 

 The opening; of the oviduct is between the ventral pieces. 

 JVlake draadaga- of the dorsal and tha l^.te^a.1 asTifipt nf thia 

 .. EgJLt fll t . h , a .-body. In the drawing of the lateral aspect 

 represent the entire abdomen, ^ake drawings of the 

 dorsal ar\^latpra,\ aspe ct of the 



PHYLUM MOLLUSCA 



I. THE PELECYPODA 



Unio, or Anodonta (Fresh Water Mussel.) 

 Study, the- empty shell. What is its shape? Of how 

 many parts or valves does It consist? How are they held 

 ^together? How does the animal rest when alive? Point 

 out the dorsal, and the ventral surfaces. Treat a small 

 piece of the shell with HCl. What is the result? gray-*- 

 surface vie w of a sin gla, valve. What is the relative posi- 

 tIon~on£e valves after the animal is taken out? Why? 

 How does the hinge act? Notice the lines of growth 

 beginning with the umbo or beak. Note the hinge teeth 

 (not present in anodonta). How do they fit when the 

 shell is closed? How many forms are there? Does the 

 color of the valve vary 'inside? Note the palial impres- 

 sions, (the line of attachments of the mantle to the shel).) 

 Note the scars for the attachment of the muscles. Ex- 

 amine the broken surface of a shell with a hand lens. 

 What attachments does the body have to the shell? Study 

 the texture of the mantle. Is it uniform in thickness? 

 The adductor muscles hold the valves together. How 

 many are there? How do' they differ In siie, and in shape? 

 The scar for the retractor pedis muscle is at the upper 

 margin of that of the adductor muscles. A little below 

 the anterior rejtractor muscle scar will be found the scar 



