EFFECT OF RADIUM ON FERTILIZATION 99 



found. Those eggs in which the germ nuclei fail to fuse do not 

 divide. 



The first striking abnormality in the growing embryos appears 

 when they are about twenty hours old. At this time the pro- 

 trochal band of cilia and the green pigment at the posterior end 

 are wholly lacking. Such embryos are of normal shape, but 

 remain motionless, while the others in the dish are swimming 

 actively about. In twenty-eight hours some are still lacking in 

 ciliation, while others have developed the ciliary ring, which 

 shows characteristic abnormalities in the distribution of the cilia. 

 Instead of being in a continuous band, they, occur in patches 

 scattered irregularly. Such embryos swim slowly, and with a 

 curious uneven motion, pursuing a devious course. In forty- 

 eight hours, when the control embryos are well provided with 

 green and red pigment and swimming vigorously at the s-urface, 

 the radium embryos are still unpigmented, or else have the pig- 

 ment broken up into small patches. The ciliation is still abnor- 

 mal. The motion is consequently abnormal, the embryos tum- 

 bling over and over, or taking a spkal course, turning on their long 

 axis. In seventy-eight hours a few of the embryos develop setae 

 and pigment, but both are abnormal. The setae rarely grow 

 out to full length, and are irregularly distributed. The majority 

 of the embryos that have survived as long as this remain in about 

 the same condition that they showed at thirty hours. 



This mode of development occurs occasionally in the controls, 

 especially if the conditions of growth are unfavorable, but never 

 in as large proportions as among the radium embryos. Unfavor- 

 able conditions obtain if many eggs are allowed to develop in 

 a small amount of water, or if they become matted together 

 after fertilization. If eggs are compressed under a coverglass 

 during early cleavage they develop precisely the same type of 

 abnormalities. 



In these embryos the effect of the injured spermatozoon remains 

 latent for many hours, and is displayed for the first time when the 

 embryo begins to differentiate the pigment and the cilia, and 

 begins to grow notably in size. 



