210 BIOLOGY: GENERAL AND MEDICAL 



exhibiting only paternal characters from the enucleated 

 egg of one species fertilized by the sperm of another. 

 This seems to be conclusive, but it is apparently offset 

 by an experiment of Kupelweiser and Loeb, who obtained 

 a larva showing no paternal characters at all from the 

 ovum of a sea-urchin, fertilized by the spermatozoon of 

 a mollusc. However, in the latter case we can be fairly 

 sure that the egg was induced to develop partheno- 

 genetically through contact with stimulating substances 

 contained in the molluscan spermatozoon, and that no 

 amphimixis took place, as the heterologous sperm cells 

 always die in an ovum of such distant relationship, and 

 the paternal chromosomes are lost in consequence. 



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. 



