212 



FIETER-BED NEMAS 



already having the substances or factors imparted by the spermatozoon, 

 or their equivalent, and we might therefore expect such eggs to be, as they are, 

 "resistant" to sperm. Whether or not this suggestion has a basis of fact, the 

 theory of cryptogenesis harmonizes with what is known about the incompat- 

 ibility of parthenogenesis and fertilization. Of course ova may be too young 

 to be fertilized, or too old to be fertilized, and their parts may be so acted upon 

 by a variety of forces as to bring them into a more responsive or less respon- 

 sive condition; needless to say, these various facts must also be taken carefully 

 into account in any such speculation as the foregoing. 



Abbreviations Used in the Illustrations 



