MULTICELLULAR ANIMALS 201 



changes during the reproductive cycle. When the ovum attains an 

 appropriate stage of maturation the foUicle opens on the surface o£ 

 the ovary and the ovum is freed. The ovary is closely invested by 

 the open end of the oviduct, called in mammals the fallopian tube. 

 The Fallopian tubes from both ovaries open into a triangular- 

 shaped cavity, the uterus, which is normally collapsed except during 

 the development of the embryo. The single posterior outlet of the 

 uterus is termed the os uteri and is normally closed by circular 

 contracted muscles. The os uteri opens outward through a short 

 canal, the vagina. A comparison of these adult structures with the 

 basic sex structures of vertebrates (Fig. 135) shows that the oviducts 

 are exclusively reproductive in function in all vertebrates and that 

 the human system differs from that of other vertebrates only in rela- 

 tively minor details. Only traces of the mesonephros are to be found 

 in the adult female. 



Suggested Readings 



Howell, W. H.: Textboo\ of Physiology. W. B. Saunders Company, 



1930. 

 Wiedersheim, H.: Comparative Anatomy of Vertebrates. Translated by 



Parker. The Macmillan Company, 1897 (out of print). 

 Walter, H. E.: Biology of the Vertebrates. The Macmillan Company, 



1928. 

 Wilder, H. H.: History of the Human Body. Henry Holt and Company, 



1923. 

 Van Cleave, H. J,: Invertebrate Zoology. McGraw-Hill Book Company, 



1931- 

 Martin, H. N.: The Human Body. Henry Holt and Company, 1926. 



Petrunkevitch, A.: Morphology of Invertebrate Types. The Macmillan 



Company, 1916. 

 Hogben, L. T.: Comparative Physiology. The Macmillan Company, 



1926. 



