REPRODUCTION 



547 



tissue closes the foramen ovale. It requires 

 a few minutes for this adjustment to take 

 place, during which time the child is bluish 

 in color, but gradually he becomes pink as 

 the circulation is separated into its pul- 

 monary and systemic parts. It is indeed 

 amazing that with all its complications this 

 process so seldom fails. 



However, if the foramen ovale does fail 

 to close or something else goes wrong with 

 the mechanism for separating the blood, 

 the baby remains bluish in color, a condi- 

 tion given the term blue baby. He is bluish 

 in color ( cyanotic ) because the oxygenated 

 and reduced blood are mixed, just as they 

 are during fetal life. Some remarkable sur- 

 gery has been accomplished in recent years 

 to correct such occasional defects. 



We have now completed the story of the 

 Rise of Anmial Life, starting with the sin- 

 gle-celled animals and culminating our dis- 



cussion with the mammals, man in particu- 

 lar. We have also considered in each group 

 how the problem of perpetuation was 

 solved, but this was always at the level of 

 an individual, a protozoan or a mammal. 

 We must now consider the problem of the 

 continuity of life in its most fundamental 

 aspects. We must attempt to answer such 

 questions as : how do genes duplicate them- 

 selves, how do cells duplicate themselves, 

 how can a sing-le cell such as a fertilized egg 

 give rise to a complex form like an earth- 

 worm or a man, and finally what underlying 

 mechanism makes it possible for a race to 

 continue apparently unchanged for many 

 generations? These are some of the most 

 peqolexing problems in biology today and 

 it is only recently that answers have begun 

 to come forth. In the next Part, Continuity 

 of Life, we shall examine some of these 

 problems and a few of the answers as we 

 know them today. 



