194 ESSENTIALS OF ZOOLOGY 



genesis may be induced in many mature eggs by change of osmotic 

 pressure due to change of salt content in the surrounding medium. 

 Fatty acids, saponin, solanin, bile salts, benzol, toluol, chloroform, 

 ether, and alcohol are other substances which will induce it. Electric 

 stimulus, mechanical prickling, and change of temperature are also 

 used. Such methods have produced artificial parthenogenesis in 

 eggs of sea urchins, starfish, molluscs, annelids, moths, and frogs. 

 The immediate cause of the development by an egg thus stimulated 

 is not known. 



In normal fertilization of an egg by only one spermatozoon, it has 

 been found that the rate of oxidation then increases from 400 to 

 600 per cent. There are indications that this is also the case in 

 artificial parthenogenesis. This oxidation may be the cause of the 

 development in the ovum. Fertilization, where it occurs, has a dual 

 function: (1) that of stimulating the egg to develop, and (2) that 

 of introducing the genetic characteristics of the male parent. 



Other features of reproduction are given in the chapter on Sexual 

 Reproduction and the Development of the Individual. 



References 



Burton-Optiz, R. : An Elementary Manual of Physiology, Philadelphia, 1936, W. 

 B. Saunders Company. 



Heilbrunn, L. V.: An Outline of General Physiology, Philadelphia, 1937, W. B. 

 Saunders Company. 



Howell, W. H.: Textbook of Physiology, Philadelphia, 1936, W. B. Saunders 

 Company. 



Macleod, J. J. R. : Physiology in Modern Medicine, St. Louis, 1938, The C. V. 

 Mosby Company. 



Rogers, C. G-. : Textbook of Comparative Physiology, New York, 1938, McGraw- 

 Hill Book Company. 



Stiles, P. G. : Human Physiology, Philadelphia, 1939, W. B. Saunders Company. 



Zoethout, W. D.: Textbook of Physiology, St. Louis, 1938, The C. V. Mosbj 

 Company. • 



