EFFECT OF RADIUM ON FERTILIZATION 97 



as follows: The moment the perforatorium becomes implanted 

 in the egg membrane there occurs the usual outflow of jelly. 

 Beneath the perforatorium there forms the usual darkly staining 

 area of protoplasm. The fertilization cone rises to meet the 

 point of attachment, then sinks, pulling the sperm head with it. 

 But as the chromatin is pulled out it is seen to be broken up into 

 irregular masses, a condition not seen in the controls. In some 

 instances the band appears to be continuous, but arranged in a 

 bead like fashion. Thus far, then, the effect of the spermatozoon 

 on the egg has been merely to fail to elicit the full response by 

 which it should be engulfed in the egg. 



During this period the egg gives off the two polar bodies in a 

 normal manner. But when the egg nucleus begins its recon- 

 struction, it fails to develop in the usual way. The chromosomes 

 increase som.ewhat in size, and each becomes surrounded by a 

 deeply staining, granular matrix. The chromatin appears nor- 

 mal. The matrix stains about as deeply as the fertilization cone. 

 Each chromosome, surrounded by the matrix, lies in a clear, non- 

 staining vacuole. Occasionally they can be seen to be segmented, 

 a condition not seen in the control. In such eggs there is a 

 total absence of astral radiations. The egg aster disappears very 

 early, and the sperm aster never develops because the sperm is 

 still entirely exterior to the egg. 



The development of the egg nucleus in such a manner is not 

 due to any poison injected into the egg by the radiated spermato- 

 zoon, but rather to the failure of the sperm head to enter. That 

 this is true may be inferred from the experiments on partial fer- 

 tilization made by Lillie ('12). These consisted of centrifuging 

 the fertilized egg at such times that the attached spermatozoon, 

 still external to the egg membrane, was removed wholly or in 

 part. In the former case, when no chromatin was introduced, 

 the eggs extruded the jelly and extruded both polar bodies. But 

 the egg nucleus, instead of forming a typical vesicle with karyo- 

 meres, failed entirely to develop, the chromosomes lying free in 

 the protoplasm. Around each chromosome was a darkly stain- 

 ing matrix, evidently corresponding to the chromosomal vesicle, 

 through no vesicular wall was formed. This condition is an 



