MOLLtrSCA. 75 



(1) the outer opening of the siphon-tube ; 



(2) the inner opening of the siphon-tube ; (Pass a 



tipped bristle through the siphon-tube and 

 make sure that you understand how the water 

 can come in around the collar and escape 

 through the siphon-tube.) 



(3) the retractor muscles, two large fleshy ridges 



attached to the siphon-tube near one end ; 



(4) the alimentary canal; (Its posterior end may 



be seen near the inner opening of the siphon- 

 tube through which the waste products of 

 digestion pass into the water.) 



(5) the ink sac, lying between the alimentary canal 



and the body Avail and probably still contain- 

 ing traces of black " ink " ; 



(6) the gills, two large feathery breathing organs. 



D. Sketches. 



1. A lateral view (10 cm.). 



2. A prepared specimen showing mantle-cavity opened 



(10 cm.). 



E. Suggestive Questions. 



1. Why does the squid take water into its mantle- 



cavity and expel it violently through the siphon- 

 tube? 



2. How would you need to modify a clam theoretically 



to make a squid out of it ? 



3. Can you see any reason why the nervous system of 



the squid should be better developed than that of 

 the clam ? 



4. What is the probable use of the pen ? 



5. What is the use of the " ink " ? 



