208 THE FROG AS AN INTRODUCTION TO MAN 



amount of water. Place where they receive the same amount 

 of light and moderate heat. Observe them daily for about ten 

 days. 



Conclusions. 1. Which lot receives the most oxygen per 

 egg ? Explain. 



2. What is the effect of oxygen on the development of 

 frogs' eggs ? 



3. WATER 



Observation. Place a few eggs in a saucer of water, and 

 an equal number from the same lot in another saucer with but 

 water enough to keep them moist. Take care that they do not 

 dry up. Place them where there are equal amounts of light 

 and moderate heat. Observe daily for about 10 days. Which 

 lot develops the better ? 



Conclusion. What is the effect of moisture on the develop- 

 ment of frogs' eggs ? 



4. FERTILIZATION 



Observation. The eggs when collected from the pond 

 have probably already been fertilized. The eggs were laid 

 in the water by the female and the males at once shed or 

 sprayed sperm cells or milt over them, thus fertilizing them. 

 Note. A thin albuminous coating immediately swells up, 

 and they stick together to form a mass in the water. If a 

 number of hens' eggs should be broken into some water, a mass 

 similar to frogs' spawn or eggs would be the result the yolks 

 corresponding to the frogs' eggs. 



Conclusions. 1. What may be the use of the gelatinous 

 mass ? 



2. Sum up the conditions necessary for the development of 



frogs' eggs. 



b. General Development (Metamorphosis) 

 Observations. 1. With models review the development of 

 an egg to the gastrula stage. Note. By the tenth day a 



