EFFECT OF RADIUM ON FERTILIZATION 101 



When massed at one point it exceeds this hmit. The explanation 

 for this phenomenon is not known. According to Lillie, the 

 extrusion of the jelly takes place when the spermatozoon be- 

 comes implanted. As the jelly diffuses outward sea water passes in 

 to take its place, so that the original size of the egg is maintained. 

 If this is true, it may be that the sea water has entered faster 

 than the jelly has been extruded, and consequently, the whole 

 layer increases in width. However, this does not explain the 

 fact that the alveolar layer is unevenly distributed. 



The increased size of the cortical layer does not persist as 

 measurements show. Within seventy minutes after fertilization 

 it has decreased noticeably, and after eighty minutes has dis- 

 appeared altogether. The following figures are average measure- 

 ments of a large number of eggs. 



Normal Radiated 



45 minutes after insemination 106 X 92/i 115 X 105ai 



60 minutes after insemination 105 X 87^ 111 X 95^ 



70 minutes after insemination 105 X 90/u 107 X 95m 



80 minutes after insemination 104 X 91m 105 X 94^ 



It is thus seen that before the first division, which occurs in 

 about ninety minutes, the eggs are of normal size. Sections show 

 that the alveolar layer by that time has entirely disappeared, 

 except in the few cases in which fertilization did not occur. 



In the control series the alveolar layer is extruded at once and 

 nothing is seen of it inside the egg forty-five minutes after insem- 

 ination. The germinal vesicle also breaks down soon after the 

 extrusion of the jelly. I found no exception to this. But in the 

 radiated eggs the vesicle shows some curious modifications in 

 behavior. It may break down at once even though the alveolar 

 layer is still present, or it may reinain intact for a considerable 

 period. In the former case, the chromatin, which, during the 

 process of dissolution of the nuclear membrane has collected in 

 the form of chromosomes, is left free in the protoplasm. If the 

 vesicle remains entire, the chromatin, which is now in granules, 

 collects along the periphery, just beneath the membrane. This 

 is the normal condition for it at this period. Occasionally the 

 granules collect in the form of chromosomes which are scattered 



THE JOURNAL OP EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 1 



