270 ZOOLOGY 



Class II. Gastropoda. Soft bodies asymmetrical ; imivalve shell or shell absent 

 Some forms breathe by gills, others by Imiglike sacs. Examples, pond snail, 

 land snail {Helix), and slug. 



Class III. Cephalopoda. Bilaterally symmetrical mollvisks with mouth sur- 

 rounded by tentacles. Shell may be external (nautilus), internal (squid), or 

 altogether lacking (octopus) . Examples, squid, octopus. 



Reference Books 



for the pupil 



Davison, Practical Zoology, pages 142-150. American Book Company. 

 Herrick, Text-hook in General Zoology, Chap. XI. American Book Company. 

 Heilprin, The Animal Life of our Seashore. J. B. Lippincott Company. 

 Jordan, Kellogg, and Heath, Animal Studies. D. Appleton and Company. 

 Morgan, Animal Sketches, Chap. XXI. Longmans, Green, and Company. 



FOR THE TEACHER 



Bulletin, U.S. Fish Commission, 1889. 



Brooks, The Oyster. Johns Hopkins Press. 



Cooke, The Mollusca, Cambridge Natural History. The Macmillan Company. 



Kellogg, The Life History of the Common Clam. Bulletin, U.S. Fish Commission 



Vol. XIX, page 193. 

 Parker, Elementary Biology. The Macmillan Company. 

 Parker and Haswell, Text-hook of Zoology. The Macmillan Company. 



