272 SEXUAL REPRODUCTION 



is known as parthenogenesis. Loeb succeeded in developing, par- 

 thenogenetically, frogs' eggs. Several reached the tadpole stage. 

 A few grew to be nearly adult in appearance and then died. 

 Their development was incomplete. Parthenogenetically devel- 

 oped organisms may have only half the number of chromosomes 

 common to the species, since no sperm chromosomes are present. 

 The process has never been performed, experimentally, in any 

 organism higher than the frog. It sometimes occurs in nature 

 in certain of the insects and certain worms. 



Questions and Suggestions 



1. What is the difference between sexual and asexual reproduc- 

 tion ? 



2. Discuss sexual reproduction in the mold ; in the Spirog^Ta. 



3. State a difference between conjugation in mold and Spirogyra. 



4. Discuss sexual reproduction in Paramecium. 



5. What is the value of sexual reproduction in the life history of 

 the Paramecium. 



6. Compare fertilization with conjugation. 



7. Discuss spermatogenesis ; oogenesis. 



8. What is the purpose of maturation ? 



9. State two cellular activities of the egg that always follow the 

 entrance of sperm. 



10. State two differences between an unfertilized and a fertilized 



11. What is parthenogenesis ? Discuss some experiments that have 

 been carried on in parthenogenesis. 



Supplementary Reading 



Atkinson, G. F., A College Textbook of Botany (Henry Holt & Co.). 



Gager, C. S., General Botany (P. Blakiston's Son & Co.). 



Holmes, S. J., An Introduction to General Biology (Harcourt, Brace & Co.). 



