374 ZOOLOGY 



interesting to the zoologist from the fact that they may represent the division of 

 fishes from which the air-breathing vertebrates sprang. One genus (Ceratodus) is 

 found in the rivers of Queensland ; the second (Protopterus) in the rivers of southern 

 Africa, and a third (Lepidosiren) in the Amazon in South America. No marine 

 forms are known. From fossil remains it is evident that the ancestors of the 

 present lung-fishes were very much more widely distributed. 



393. Supplementary Studies for Library and Field. 



1. What are the theories as to the origin of the paired fins of fishes? 



2. In what way do fishes change their long axis from the horizontal position 

 so as to ascend or descend obliquely in swimming ? 



3. Range of size in fishes. 



4. Probable origin of fresh-water fishes. What forms are now able to pass 

 back and forth from fresh to salt water? 



5. Accumulate data concerning the habitat, food, breeding habits, distribu- 

 tion, economic importance (with the reasons therefor) of some of the following 

 fishes: salmon, trout, white-fish, sunfish, muskalonge, herring, eel, cod, flat-fish, 

 mackerel, shark, ray, sturgeon, gar-pike, bowfin. 



6. What is known of the habits of the lung-fishes calculated to suggest how the 

 lung may be of value in preserving the life of the animals? 



7. Migrations among fishes. 



8. Parental care among fishes. 



9. The number of eggs produced by various species. 



10. Study figures showing the embryology of the salmon or other bony fish. 



11. The blind fishes found in caves. What are the principal facts concerning 

 them, and what explanations have been offered to account for their habits and 

 modifications. 



12. Collect all the data possible concerning the flat-fishes. 



13. Examine all the figures of fishes found in your library, and make note of 

 the chief points of variation and the range of these. 



