PROBLEMS OF FERTILIZATION 



usually completed before the cortical changes are evident. 

 These changes are the most obvious indicia of successful 

 insemination, and, as they are usually accepted in exper- 

 imental parthenogenesis as indications of initiation of 



FIG. 4. a and b, penetration of the spermatozoon in the oligochaete 

 Rhynchelmis (after Vejdovsky and Mrazek). Note the extensive yolk- 

 free cone produced in the egg cytoplasm, c, Spermatozoon in the egg 

 of the bat VespertiUo noctula (after Van der Stricht). The entire sper- 

 matozoon enters, d, The spermatozoon in the egg of the snail Physa 

 fontinalis (after Kostanecki and Wierzejsky). The long coiled tail of 

 the spermatozoon lies in the egg cytoplasm; sperm centrosomes with 

 aster between tail and head. 



development, it is important to describe them. They 

 are of great significance for the physiological problems 

 which are considered later, and we must examine them 

 with a view to distinguishing the general from the more 

 special features. 



