240 NEIL S. DUNGAY. 



tion of the chromatic nucleoli without true fertilization. In some 

 cases the chromosomal vesicles seem to dissolve in the cytoplasm, 

 leaving behind several small chromatic nucleoli. 



To sum up, the sperm attaches itself to the egg which slowly 

 undergoes maturation but does not form jelly or segment. The 

 sperm does not enter the egg and no fertilization cone is formed. 

 After the formation of the second polar body, the chromosomal 

 vesicles of the egg nucleus form and, failing to unite with a 

 sperm nucleus, undergo degenerative changes. The spermato- 

 zoon thus gives the egg a stimulus which induces only the forma- , 

 tion of the polar bodies. In such cases the maturation process 

 goes on in a normal manner with the exception of a retardation 

 in the rate. This retardation is probably caused by the reten- 

 tion of the jelly-forming materials in the cortical layer of the egg, 

 which would tend to cut down the rate of exchange with the 

 external medium. 



It is possible that we are dealing in this case with eggs which 

 require a rather high degree of stimulation in order to produce 

 jelly. Observation on unfertilized eggs shows that there is a 

 considerable degree of variation in the amount of stimulus 

 required to produce jelly formation. It may be that the injured 

 sperm cells are incapable of giving so great a stimulus for jelly 

 formation as do the normal ones and that some of the eggs can- 

 not respond to the slight stimulus given, by emptying their 

 cortical alveoli, although they may be able to form polar bodies. 

 Whether the cause lies in the egg or in the sperm it is necessary, 

 since these eggs develop normally if fertilized with uninjured 

 sperm, to assume that the injury to the developmental process is 

 produced by the action of external influences upon the sperm 

 cell before the time of insemination. It is also clear that in the 

 case of Nereis eggs maturation may take place without jelly 

 formation. 



(a 2) In a much larger number of cases the eggs go a step farther 

 than those described above. The living material shows eggs 

 which undergo both maturation and jelly formation but which 

 never segment. Although, in the earlier stages, a sperm cell 

 may be seen to be attached to the vitelline membrane no fertiliza- 

 tion cone is present. Examination of the sections of such eggs 



