EFFECT OF RADIUM ON FERTILIZATION 91 



the chromatin. The destruction of the poison by prolonged ra- 

 diation makes it possible for the egg to develop parthenogeneti- 

 cally. When the fertilized egg is radiated enough poison is gen- 

 erated to prevent cell division entirely. 



There is no doubt that some substance is stimulated to activity 

 under the influence of radium radiations which acts like a poison 

 in that it produces the apparent abnormalities, and that this sub- 

 stance is intimately connected with the nucleus. But to call this 

 substance a 'contagium vivo' and to endow it with the property 

 of producing the observed results does not aid in the solution of 

 the problem. The solution must be fundamentally chemical in 

 nature, even though the precise reactions involved cannot now be 

 discovered. 



The following investigation was made to find how the early 

 development of the egg is affected by radium radiations when (1) 

 the sperm is exposed; (2) when the egg is exposed; and (3) when 

 the egg is exposed immediately after insemination. The problem 

 was suggested by Prof. T. H. Morgan, to whom I take pleasure 

 in expressing my thanks. 



METHODS 



Nereis limbata was used in these experiments. In its sexual 

 phase it can be obtained in great numbers during the summer 

 months at Woods Hole, Massachusetts. This material has a 

 great advantage in that practically 100 per cent of the eggs 

 segment and develop normally under appropriate conditions, 

 showing great regularity in the rate of development. The sex- 

 ually mature individuals swarm in great numbers at the surface 

 of the water on dark evenings, and can be kept, with proper pre- 

 cautions for many hours before they discharge their sexual prod- 

 ucts. For each experiment the eggs of two females were used. 

 It was found necessary to work with small quantities of eggs since 

 the jelly which the eggs extrude at the time of insemination is very 

 mucilaginous and tends to mat together, in which event the eggs 

 fail to develop normally. To prevent this it is necessary to stir 

 them frequently during the first fifteen minutes, at the end of 



