434 How A?iinials afid Flmits Reproduce unit viii 



the babies of grazing animals are much 

 more independent. They are able to 



learning. The young mature so slowly 

 that family life continues for many 



stand, even to ^\■alk awkwardly, and are 

 \\ell protected by a coat of hair. 



Family life in animals. Among animals 

 that are born or hatched in so immature 



years. 



Successful reproduction. All species 

 now in existence are successful in pro- 

 ducing offspring that survive. If not, the 

 a state that they cannot obtain their own species would have died out long ago. 



food there is found some kind of family 

 life. This is true of most birds and of 

 mammals. And where there is family life 

 the number of offspring is always com- 

 paratively small. 



Family life may continue for many 

 weeks or even years, as among elephants 

 and human beings. In such cases parental 

 care means much more than supplying 

 food and hiding the offspring. The 

 young have an opportunity to learn how 

 to get along in the world. When the lion 

 drags wounded prey to its lair, the cub 

 learns to tear the flesh. To what extent it 

 watches and imitates its parents is not 

 known, but at least it practices the use 

 of claws and teeth. Among apes and espe- 

 cially among human beings there is much 



In the more complex animals, as you 

 have just read, the number of offspring 

 is relatively small but the parents protect 

 and feed the young. In some other ani- 

 mals the eggs and embryos and young;' 

 are fitted in one or more ways to survive 

 the dangers to which they are exposed. 

 Yet in many species there is no protec- 

 tion of any kind and the possibilities for 

 destruction are very great. These species 

 survive because they reproduce in enor- 

 mous numbers. A female cod, for ex- 

 ample, may lay 8,000,000 eggs every 

 season. If only one male and one female 

 of that 8,000,000 grow up and repro- 

 duce, the species is provided for. If 

 larger numbers grow up and reproduce, 

 the species will be on the increase. 



Questions 



1. What are the male reproductive organs called? What are the female 

 organs called? What causes secondary sex characters? Give examples 

 of secondary sex characters in birds, in deer, and in man. 



2. Describe the sex organs of a male and female frog. 



3. Name the male and female gametes. How do they differ from each 

 other in structure and in size? 



4. Describe spawning and fertilization in fish. What name is given to a 

 fertilized egg? State three ways in which it differs from an unferti- 

 lized t^^. 



5. Give two examples among insects of development of the t^g without 

 fertilization. 



6. By what tMO methods did Jacques Loeb obtain parthenogenetic ani- 

 mals? 



7. Describe the cell divisions which immediately follow fertilization. 

 Describe the changes that occur in the mass of cells. What is an 

 embryo? 



