Reproduction in Multicellular Animals - 397 



17. Adrenalin injected into the maternal blood 

 stream accelerates the heartbeat of the fetus 

 as well as of the mother. Explain. 



18. Trace a sample of blood from the umbilical 

 artery to the umbilical vein (Fig. 21-1 ID). 



19. For each of the following substances, state 

 whether it tends to pass (a) from the mater- 

 nal to the embryonic blood, or (b) from the 

 embryonic to the maternal blood, in the 

 capillary system of the placenta: (1) glucose; 

 (2) CO a ; (3) urea; (4) 2 . 



20. What is the afterbirth? How does it differ in 

 different mammals? 



21. Specify two kinds of nonplacentate mammals. 

 Explain why such creatures undoubtedly 

 found difficulty in competing with the mod- 

 ern mammals. 



22. Distinguish between: (a) budding and fission; 

 (b) identical and fraternal twins; (c) com- 

 plete and incomplete embryonic fission. 



23. Discuss the possible relation between fission 

 and segmentation. 



FURTHER READINGS 



Ourselves Unborn, by George W. Corner; 

 New Haven, 1944. 



Atlas of Human Anatomy, by Frohse, Broe- 

 del, and Schlossberg; New York, 1950. 



3. The Living Body, by C. H. Best and N. B. 

 Taylor; New York, 1958. 



4. The Srienee of Human Reproduction, by 

 H. M. Parshley; New York, 1933. 



