PROBLEM 2. How More Complex Animals Reproduce 435 



8. Name the three germ layers and state which organs or tissues are 

 formed from each. 



9. How does the fish embryo get food while the organs for food-getting 

 and locomotion are in the process of development? When is the em- 

 bryo stage completed? 



ID. Which orfTans are the last to be fully developed? When and how do 

 these organs originate? 



11. Is protection of the eggs or young the usual or unusual condition in 

 fish? Cite exceptions. 



12. When, where, and how are frog eggs fertilized? Give the important 

 stages in the metamorphosis of the frog. 



13. How does fertilization in land-living animals differ from that in the 

 fish or frog? How is internal fertilization an advantage to the species? 

 Give examples of instinctive behavior in connection with care of eggs. 



14. Why is the thick shell of the bird's egg no hindrance to the entrance 

 of the fertilizing sperm? What in fish development corresponds to the 

 yolk of the hen's egg? Describe and explain the origin of each part 

 of the bird's egrg. How long does chick development take? What care 

 is taken of the eggs during this time? 



15. Describe some of the instinctive behavior shown by young and par- 

 ent birds. 



16. Compare reproduction in mammals and fish as to: (a) fertilization, 

 (b) development of embryo, and (c) food and oxygen used by 

 embryo, 



17. Using all the terms given, explain where the rabbit embryo develops, 

 how it is protected, and exactly how it receives food and oxygen. 



18. In what respect is the care of all mammals the same? How does the 

 care differ among various mammals? Give examples. 



19. What relation is there between family life and the number of off- 

 spring? 



20. If codfish, for example, are not on the increase what proportion of the 

 female gametes develop and grow to maturity? What might be the 

 result if the codfish produced fewer eggs? 



Exercises 



1. How may the sexes be distinguished in some birds? Examine pictures 

 or specimens of both sexes of various species of birds. What differences 

 do you note between male and female? Can you see any advantage in hav- 

 ing' the female less brightly colored? If pictures are available, trace the 

 outline of the birds through glass and color with crayons or paint. 



2. Deinonstration. The reproductive organs of the frog. Study freshly 

 killed or, if necessary, preserved male and female frogs. Compare the ex- 

 ternal appearance. Can you distinguish male from female? During the 

 breeding season the male has enlarged thumbs. Are they visible? How can 

 the sexes be distinguished after dissection? How many spermaries has the 



