PROBLEM 146 167 



which fit it for the life it leads. Explain exactly how each struc- 

 ture you have described is an adaptation. 



b. The Bullfrog Group 



Show three ways not mentioned in the last question in which the 

 bullfrog is fitted or adapted to its environment. At what time of 

 year do frogs deposit their eggs ? How does it compare with 

 that of the toad? (See the toad group.) How do you account 

 for the presence of the large tadpoles found swimming about? 



What might be some of the enemies of the bullfrog ? How might 

 it escape from its enemies ? Explain exactly how a frog catches an 

 insect. Compare the habitat of the bullfrog with other amphib- 

 ians found in the groups in this alcove. How is it similar and 

 how does it differ? 



Problem 146 : To collect and study frogs' eggs. 



Materials. — Trip to shallow fresh-water pond. Battery jars 

 or aquarium. 



Method. — Look for eggs in shallow fresh- water ponds late in 

 March or early in April. Collect some eggs and place them in a 

 shallow aquarium with some algae in a sunny place. 



Observations. — Notice that the eggs look like little black 

 dots in a mass of jelly. Is their color uniform? 



The collected eggs have probably been fertilized. They were 

 laid in the water by the female ; the males fertilizing them by plac- 

 ing sperm cells on them, as soon as the eggs were laid. After 

 laying, the thin albuminous coating with which they are covered 

 swelled up and they stuck together. 



Examine some of the eggs under a magnifying glass. Some of 

 them have probably begun to segment (divide into many cells). 

 Which side of the egg, the black or white side, seems to be broken 

 into smaller cells? 



NOTE. — The white side is filled with yolk, or food. 



Conclusion. — Write a paragraph telling where frogs lay eggs, 

 how the eggs are fertilized, and how they are protected after 

 fertilization. 



