EFFECTS OF RAYS OF RADIUM ON PROTOPLASM 335 



in the center of the egg when the metaphase of the second 

 spindle has formed. The pronuclei fuse about 65 minutes after 

 insemination. 



The second column shows the rate at which these phenomena 

 occur in unfertilized eggs which have been exposed to the rapid 

 beta rays acting at a distance of 50 mm. The perivitelline 

 space is not appreciably widened. The sperm enters about 

 thirty minutes after insemination, that is, about 15 minutes 

 ahead of the control. In the meantime the first anaphase has 

 developed. In other words, the development of the egg has kept 

 pace with the early entrance of the sperm. By the time the 

 sperm is in the center of the egg (in 40 min.) the first polar body 

 has been extruded and the second metaphase figure has developed. 

 Here again, the whole development occurs at exactly the same 

 rate as in the controls. If the living eggs only had been observed 

 the conclusion might have been drawn that the treatment with 

 radium stimulated the eggs to divide at a faster rate than normal. 

 But the cytological evidence just presented shows that there 

 has been no stimulation. The weakened egg membranes have 

 permitted the sperm to be drawn in earlier than usual, but that 

 is all. There are no constant abnormalities to be found in these 

 eggs either during the maturation divisions or during cleavage. 

 The subsequent development is normal, but the larvae develop 

 at a slower rate than the control animals. The effect of these 

 rays under these conditions is therefore to weaken the egg 

 membranes and to bring about a retardation in the growth of the 

 embryo. 



The effect of the slow and rapid beta rays is shown in the third 

 column. The perivitelline space, which at first is of normal 

 width, increases later in a striking manner which has already 

 been described. The protoplasm at the periphery of the egg is 

 much changed in appearance. The finely granular character 

 seen in normal eggs, is lacking, and in its place is a fairly homo- 

 geneous substance in which are held numerous faintly staining 

 spherules (fig. 3) . Occasionally it presents a vacuolated appear- 

 ance seen in figure 4. As the perivitelline space increases in 

 width the entrance cone is also pulled out so that it stretches 



