198 BIOLOGY: GENERAL AND MEDICAL 



In order that ova shall develop they must ordinarily 

 be fertilized, but this is not in all cases essential. J. 

 Loeb has done much to convince us that the stimuli that 

 lead to development are chemical or mechanical, and has 

 experimentally treated a variety of unfertilized eggs in 

 such manner as to bring about artificial parthenogene- 

 sis. In natural sexual fertilization the spermatozoon 

 accomplishes the double purpose of furnishing the neces- 

 sary stimulus at the same time that it effects amphimixis, 

 and thus affords opportunity for the variation of the 

 species. 



REFERENCES. 

 Same as for Chapter VII. 



