EFFECT OF RADIUM ON DEVELOPMENT OF CH.ETOPTERUS. 55 



The significant feature in these experiments is the sudden drop 

 in the rate of cleavage seen in eggs radiated for periods up to 

 40 minutes. The explanation for this phenomenon is to be 

 found in the behavior of the egg nucleus during maturation and 

 subsequent growth, and in the behavior of the sperm nucleus 

 during cleavage. 



CYTOLOGICAL OBSERVATIONS. 



A cytological examination of eggs exposed for periods of 15 to 

 35 minutes previous to insemination shows that the first effect of 

 the radium radiations is on the chromatin; the protoplasm is not 

 visibly affected. The abnormal behavior of the egg nucleus is 

 perfectly apparent, but even prolonged radiation produces no 

 visible change in the protoplasm. Without doubt the latter is 

 affected, for polyspermy becomes more and more common as the 

 duration of the exposure is lengthened. In Nereis, polyspermy 

 under these conditions is due to a weakening of the egg membrane 

 and perhaps to a partial liquefaction of the protoplasm. The 

 same explanation may hold true for Chcetopterus also. 



All the eggs exposed for periods up to 35 minutes show the 

 same types of abnormalities but in varying degrees, the more 

 pronounced being found naturally in eggs exposed for the longer 

 periods. The outstanding feature in the development of these 

 eggs is the ever increasing tendency of the germ nuclei to remain 

 apart. This is not due to any unusual development of the sperm ; 

 its centrosome divides normally, the asters appear, and the whole 

 apparatus moves inward at the usual rate (Fig. i). But the egg 

 nucleus often remains close under the region of the polar bodies 

 and may even be connected with them by a protoplasmic bridge 

 in which chromatin threads can be distinguished. This pheno- 

 menon grows more common as the duration of the exposure is 

 increased to 35 minutes. In this position it develops more or 

 less normally, depending on the length of exposure. During 

 cleavage the egg chromatin always remains separate from the 

 dividing sperm chromosomes and can easily be distinguished 

 from them because of its position and appearance. With this 

 brief statement of the general course of development in the ra- 

 diated eggs we may now examine in detail some of the conditions 

 found during the various stages of maturation and cleavage. 



