168 THE FISH AND FROG 



Problem 147 : To study conditions favorable for development 

 of frogs' eggs. 



Materials. — Live frogs' eggs, glass dishes. 



a. Temperature 



Method. — Place some eggs in shallow dishes. Place one lot in 

 a moderately warm room, another in a cold room, and a third in 

 an ice box. 



Observations. — Watch and record results daily for two weeks. 



Conclusion. — What is the relation between temperature and 

 the development of frogs' eggs ? 



b. Oxygen 



Method. — Place a large number of eggs in a dish containing 

 one quart of water. Place a few eggs from the same egg mass in 

 another dish containing a like amount of water. Place both 

 dishes where they receive the same conditions of light and heat. 



Observations. — Make and record operations daily for two 

 weeks. 



Conclusion. — 1. Which lot receives the more oxygen per egg? 

 Explain. 



2. Does oxygen affect the development of frogs' eggs? 



Problem 148: To study the metamorphosis of the frog. 



Materials. — Wax models of development of frog, living or 

 preserved specimens of various stages, charts, and young and old 

 stages of tadpoles in shallow dishes. 



Method and Observations. — Using the wax models, try to find 

 the chief differences in the development of this egg as compared 

 with the egg without any yolk. Can you find any gastrula stage 

 here? Look at the model cut in section to answer this point. 

 (See also page 245, Civic Biology.) 



Trace the changes from the time the egg segments to the time 

 it becomes a free-swimming tadpole. Where are the gills located 

 at first? What kind of mouth parts does the tadpole seem to 

 have? Notice the sucker and the horny jaws. 



How would the early stage of the tadpole breathe ? What sort of 



