328 CHARLES PACKARD 



reached the objects. All experiments of this sort were negative, 

 showing that the gamma rays in passing through even a short 

 layer of air, lose much of their effectiveness. 



b. The beta rays 



I. Experiments on Nereis. The effect of the rapid beta rays, 

 acting at about 50 mm. distance, is seen in a change both in the 

 division rate and in the physical properties of the protoplasm. 

 After the first cleavage the blastomeres divide at a slower rate 

 than normal, although the mode of division is perfectly regular. 

 The swimming trochophores are normal and as active as the 

 controls, but are always behind the controls in their stage of 

 development. The first cleavage occurs before the control eggs 

 divide, but this apparent acceleration is due to the weakening of 

 the peripheral protoplasm of the egg and not to an acceleration 

 of metabolic processes. 



When unfertilized eggs are placed directly above the radium, 

 at a distance of 4 mm. the effect is far different. If the rapid 

 beta rays are used alone, the peripheral layers of protoplasm 

 are chiefly affected. If both rapid and slow beta rays are used 

 the egg quickly dies, usually before the first cleavage. In the 

 first case there is a profound change in the mode of extrusion of 

 the egg jelly. 



The normal extrusion of jelly, which has been described by 

 Lillie ('11), takes place as follows: As soon as a sperm becomes 

 implanted in the vitelline membrane the jelly, which has been 

 held in delicate alveoli in the cortical layer of the egg, begins to 

 pass through the membrane forming a thick layer outside of the 

 egg. The alveoli, which have thus been emptied of their con- 

 tents, later become filled with water so that they almost dis- 

 appear from view. But before this occurs their walls may be 

 seen extending radially out to the membrane of the egg. 



In the radiated eggs no change can be noted before insemi- 

 nation. The oil droplets and the mitochondria, which can be 

 seen by dark field illumination, are normal. After insemination 

 the jelly is given off, but it has not the usual sticky character, 



