REPRODUCTION 



115 



bility that some of the offspring may be better adapted to survive than 

 either parent was. 



33. Asexual Reproduction 



Asexual reproduction occurs commonly in plants, protozoa, coelen- 

 terates, bryozoa and tunicates, but may occur even in the highest animals. 

 The production of identical twins by the splitting of a single fertilized 

 egg is a kind of asexual reproduction. The splitting of the body of the 

 parent into two more or less equal daughter parts, which become new 

 whole organisms, is called fission. Fission occurs chiefly among single- 



Zygote 



Sexrual ^eneraJbion— \ 



Sporula-tion. 



Saiivajy 6la-nd. 

 Sporozoite 



a-metocytc 



Sporula.tion 



Figure 6.1. A diagram of the life cycle of the malaria parasite, Plasmodium. An in- 

 fected mosquito bites a man and injects some Plasmodium sporozoites into his blood 

 stream. These reproduce asexually by sporulation within the red blood cells of the host. 

 The infected red cells rupture and the new crop of merozoites released then infects other 

 red cells. The bursting of the red cells releases toxic substances which cause the periodic 

 fever and chill. In time some merozoites become gametocytes which can infect a mosquito 

 if one bites the man. The gametocytes develop into eggs and sperm and undergo sexual 

 reproduction in the mosquito, and the zygote, by sporulation, produces sporozoites which 

 migrate to the salivary glands. 



